SEO is the set of practices aimed at increasing a website's organic visibility in search engine results pages (SERPs). It encompasses on-page optimizations (content, HTML), off-page optimizations (link earning) and technical work (speed, site structure). Organic rankings are achieved without paying the search engine for placement.
SERP (Search Engine Results Page)
The SERP is the page a search engine returns in response to a user query. It can include organic results, paid ads, featured snippets, Knowledge Panels, images, videos, local packs and other rich formats. Analysing the SERP for a target keyword reveals the search intent and the type of content Google already rewards.
Keyword
A keyword is a term or phrase that users type into search engines. Keywords are classified by search volume (estimated monthly frequency), difficulty (KD - competitive difficulty for organic ranking) and intent (informational, navigational, transactional, commercial). Keyword selection is the foundation of any SEO strategy.
Search Intent
Search intent is the underlying reason why a user performs a particular query. The four main intent categories are: informational (wants to learn), navigational (wants to reach a specific site), transactional (wants to buy or act) and commercial/investigational (wants to compare before deciding). Aligning content to intent is a prerequisite for ranking.
Crawling
Crawling is the process by which search engine bots (crawlers or spiders, such as Googlebot) visit web pages by following links to discover and collect content. The frequency with which a site is crawled depends on its authority, update rate and the crawl budget allocated by the search engine.
Crawl Budget
Crawl budget is the number of URLs that Googlebot is willing to crawl on a site within a given time period. A limited crawl budget can prevent important pages from being indexed. It is managed via robots.txt, XML sitemaps, reducing duplicate URLs, canonicalisation and fixing 404 errors and redirect chains.
Indexing
Indexing is the process by which a search engine analyses and stores the content of a web page in its database (the index) after crawling. A page must be indexed to appear in the SERPs. The tag and the robots.txt file control which pages are excluded from the index.
Ranking
Ranking is the position of a web page in the SERP for a specific keyword. Ranking algorithms evaluate hundreds of signals - content relevance, backlink quality, Core Web Vitals, HTTPS security, E-E-A-T signals - to order results. The first organic position historically attracts the largest share of clicks.
Backlink
A backlink (or inbound link) is a hyperlink from an external website pointing to a page on your own site. Backlinks from authoritative and topically relevant sources are a strong ranking signal. Quality (authority of the source domain, relevance of the context) matters more than quantity.
Anchor Text
Anchor text is the clickable text of a hyperlink. Search engines use anchor text to understand the topic of the destination page. A natural anchor text profile includes brand variants, bare URLs, descriptive anchors and generic anchors. Excessively optimised exact-match keyword anchor texts can attract penalties.
Domain Authority (DA)
Domain Authority is a proprietary Moz metric (scale 1-100) that estimates a domain's ability to rank in search engines. It correlates with but is not equivalent to Google's PageRank. It is used as a proxy to assess site authority in competitive analyses. It is not a direct Google ranking signal.
Page Authority (PA)
Page Authority is a Moz metric (scale 1-100) estimating the ranking strength of a single page. Like DA, it is a comparative indicator useful for prioritising link building and on-page optimisations; it is not an official Google metric.
Canonical Tag
The canonical tag () tells a search engine the preferred URL when duplicate or very similar versions of the same page exist. It prevents link equity dilution across multiple URLs and duplicate content issues. It should point to the definitive URL intended for indexing and ranking.
XML Sitemap
An XML sitemap is a file listing a site's URLs and optionally providing metadata (last modification date, update frequency, priority). It helps crawlers discover important pages, especially on large sites or those with a weak internal link structure. It should be registered in Google Search Console.
Robots.txt
The robots.txt file is a text file in the site's root directory that specifies instructions to crawlers about which pages or directories not to crawl (Disallow directive). It is not a security mechanism and does not guarantee that pages are not indexed if they are linked from external sources. To block indexing, use the noindex tag.
Meta Description
The meta description is the HTML attribute that provides a brief summary of a page's content. While not a direct ranking signal, it influences organic click-through rate because Google often displays it as the snippet in the SERP. It should be unique per page, relevant and compelling enough to encourage clicks.
Title Tag
The title tag is the HTML </code> element that defines the page title shown in the browser tab and as the first clickable element of the organic result in the SERP. It is one of the most important on-page ranking signals. It should contain the primary keyword near the beginning, be unique per page and have an optimal length of 50-60 characters.</p><p><h2 id="h2-17-ctr-click-through-rate">CTR (Click-Through Rate)</h2></p><p>CTR is the ratio of clicks to impressions, expressed as a percentage. In organic SEO it is monitored via Google Search Console. A CTR above average for a given position is a potential positive signal for the algorithm.</p><p><h2 id="h2-18-conversion">Conversion</h2></p><p>A conversion is the completion of a desired action by a user, such as a purchase, form submission, newsletter sign-up or phone call. Conversion rate (CVR) is the ratio of conversions to sessions or unique visitors. It is the ultimate metric linking traffic to business outcomes.</p><p><h2 id="h2-19-marketing-funnel">Marketing Funnel</h2></p><p>The marketing funnel describes the theoretical user journey from first brand awareness to purchase and beyond. Classic stages are Awareness, Interest, Consideration, Intent, Conversion and Loyalty. Each stage requires different content types and tactics.</p><p><h2 id="h2-20-attribution-model">Attribution Model</h2></p><p>An attribution model is the rule that assigns credit for a conversion to the various touchpoints in the user journey. Main models include: last click (all to final channel), first click (all to first), linear (equally distributed), time decay (more weight to later touchpoints) and data-driven (based on statistical data). Model choice impacts budget decisions.</p><p><h2 id="h2-21-cpc-cost-per-click">CPC (Cost Per Click)</h2></p><p>CPC is the amount an advertiser pays each time a user clicks on an ad. In PPC platforms like Google Ads, the effective CPC depends on the auction, ad quality (Quality Score) and the maximum bid. Average CPC varies greatly by industry and keyword.</p><p><h2 id="h2-22-cpm-cost-per-mille">CPM (Cost Per Mille)</h2></p><p>CPM is the cost per thousand ad impressions. It is the typical pricing metric for branding and display advertising campaigns where the goal is visibility rather than direct clicks. Calculated as total campaign cost divided by impressions multiplied by 1,000.</p><p><h2 id="h2-23-roas-return-on-ad-spend">ROAS (Return on Ad Spend)</h2></p><p>ROAS measures the revenue generated per euro spent on advertising: <code>ROAS = Campaign Revenue / Ad Spend</code>. A ROAS of 4 means €4 in revenue for every €1 invested. It does not account for operating costs, unlike ROI which is a comprehensive profitability metric.</p><p><h2 id="h2-24-cpa-cost-per-acquisition">CPA (Cost Per Acquisition)</h2></p><p>CPA measures the average cost to obtain a single conversion (sale, lead, app install or any defined KPI): <code>CPA = Total Spend / Number of Conversions</code>. <strong>CPA is not the same as CAC (Customer Acquisition Cost)</strong>: CPA can refer to any type of conversion including non-customer conversions, whereas CAC specifically measures the cost of acquiring a new paying customer and typically includes all marketing and sales costs.</p><p><h2 id="h2-25-cac-customer-acquisition-cost">CAC (Customer Acquisition Cost)</h2></p><p>CAC is the average cost to acquire a single new paying customer: <code>CAC = Total Marketing + Sales Spend / New Customers Acquired in Period</code>. Unlike CPA - which can cover any type of conversion - CAC is specific to paying customers and typically includes all marketing, sales and onboarding costs. The LTV/CAC ratio indicates the economic sustainability of acquisition.</p><p><h2 id="h2-26-ltv--clv-lifetime-value--customer-lifetime-value">LTV / CLV (Lifetime Value / Customer Lifetime Value)</h2></p><p>Lifetime Value is the total expected revenue (or margin) from a customer over the entire business relationship: <code>LTV = Average Order Value × Purchase Frequency × Relationship Duration (years)</code>. The LTV/CAC ratio guides acquisition investment decisions: a ratio below 3 often signals an unsustainable cost structure.</p><p><h2 id="h2-27-roas-vs-roi">ROAS vs ROI</h2></p><p>ROAS (<code>Revenue / Ad Spend</code>) measures the effectiveness of the advertising campaign alone without considering product costs. ROI (<code>(Net Profit - Investment) / Investment × 100</code>) is a comprehensive profitability measure including all costs. A high ROAS does not guarantee positive ROI if product or operational costs are high.</p><p><h2 id="h2-28-core-web-vitals-cwv">Core Web Vitals (CWV)</h2></p><p>Core Web Vitals are a set of metrics defined by Google to quantify perceived user experience on a web page. They are: LCP (Largest Contentful Paint - loading speed of the main content), INP (Interaction to Next Paint - input responsiveness) and CLS (Cumulative Layout Shift - visual stability). They are confirmed Google ranking signals.</p><p><h2 id="h2-29-lcp-largest-contentful-paint">LCP (Largest Contentful Paint)</h2></p><p>LCP measures the time needed for the largest and most visually relevant content of a page (hero image, H1 heading, text block) to be rendered in the visible browser area. Google considers an LCP below 2.5 seconds good. Optimised through fast servers, proper lazy loading, preloading critical resources and image optimisation.</p><p><h2 id="h2-30-inp-interaction-to-next-paint">INP (Interaction to Next Paint)</h2></p><p>INP measures the overall latency of user interactions (clicks, taps, key presses) during the entire page visit, replacing FID from March 2024. Google considers an INP below 200 ms good. Improved by reducing main thread work (long tasks), code splitting and using Web Workers.</p><p><h2 id="h2-31-cls-cumulative-layout-shift">CLS (Cumulative Layout Shift)</h2></p><p>CLS quantifies unexpected layout shifts during page load: elements moving while users are reading or clicking. A CLS above 0.1 is considered needing improvement. Common causes are images without declared dimensions, dynamic insertion of banners or ad-injected content, fonts with different dimensions from the system font.</p><p><h2 id="h2-32-schema-markup-structured-data">Schema Markup (Structured Data)</h2></p><p>Schema markup is a microdata vocabulary (schema.org) embedded in HTML to explicitly describe the type and content of a page (product, article, FAQ, recipe, event) to search engines. It enables rich results (rich snippets, knowledge panels, carousels) in the SERP. Google supports JSON-LD (recommended), Microdata and RDFa.</p><p><h2 id="h2-33-featured-snippet">Featured Snippet</h2></p><p>A featured snippet is a "position zero" result that Google displays above standard organic results, extracting a text excerpt, table or list from a web page to directly answer the query. Capturing a featured snippet can significantly increase CTR even from positions 1-5. Optimised by structuring content with clear question-answer format and targeted H2/H3 headings.</p><p><h2 id="h2-34-link-equity-link-juice">Link Equity (Link Juice)</h2></p><p>Link equity (or link juice) is the value and authority that a backlink transfers from a source page to the destination page. The amount of link equity depends on the authority of the source page, the number of outbound links on that page and the <code>rel</code> attribute (dofollow vs nofollow). Internal links redistribute link equity within the site.</p><p><h2 id="h2-35-nofollow">Nofollow</h2></p><p>The <code>rel="nofollow"</code> attribute on an <code><a></code> tag signals to search engines not to transfer link equity to the destination page and not to follow that link for ranking purposes. Used for editorially unendorsed links (comments, guest posts, ads), sponsored links (<code>rel="sponsored"</code>) or user-generated content (<code>rel="ugc"</code>). Google treats it as a "hint", not an absolute instruction.</p><p><h2 id="h2-36-301-redirect">301 Redirect</h2></p><p>A 301 redirect (permanent redirect) tells browsers and crawlers that a page has been permanently moved to a new URL. It passes most of the link equity to the destination page. Used to consolidate duplicate URLs, change site structure or migrate to a new domain. A 302 redirect (temporary) does not transfer link equity in the same way.</p><p><h2 id="h2-37-duplicate-content">Duplicate Content</h2></p><p>Duplicate content refers to substantially identical or very similar text appearing on multiple URLs of the same site or across different sites. It can cause confusion about which URL to index and dilute link equity across variants. Managed with canonical tags, 301 redirects or URL parameters in Google Search Console.</p><p><h2 id="h2-38-e-e-a-t">E-E-A-T</h2></p><p>E-E-A-T (Experience, Expertise, Authoritativeness, Trustworthiness) is the framework used by Google Quality Raters to evaluate content quality and the credibility of those who produce it. Introduced as E-A-T in 2018 and updated with the "E" for Experience in 2022. Particularly relevant for YMYL (Your Money Your Life) content.</p><p><h2 id="h2-39-ymyl-your-money-your-life">YMYL (Your Money Your Life)</h2></p><p>YMYL refers to pages covering topics that can significantly impact a person's health, safety, financial situation or happiness. Google applies higher E-E-A-T quality standards to this type of content. Examples include financial news, medical guides, legal sites and e-commerce.</p><p><h2 id="h2-40-hreflang">Hreflang</h2></p><p>The hreflang attribute is an HTML tag (<code><link rel="alternate" hreflang="..."></code>) signalling to search engines the language and geographic variant of a page, helping them serve the correct content to users based on their language and location. Essential for multilingual or multi-regional sites to avoid international duplicate content issues.</p><p><h2 id="h2-41-sitelinks">Sitelinks</h2></p><p>Sitelinks are the additional links shown beneath the main result in the SERP for brand or navigational searches. They are algorithmically generated by Google based on site structure, internal links and user behaviour. Not directly controllable but can be influenced through site structure and internal linking.</p><p><h2 id="h2-42-keyword-cannibalization">Keyword Cannibalization</h2></p><p>Keyword cannibalization occurs when multiple pages on the same site compete for the same target keyword, diluting link equity and confusing Google about which URL to rank. Resolved by consolidating content into a single page, using canonical tags or clearly differentiating the focus of each page.</p><p><h2 id="h2-43-internal-linking">Internal Linking</h2></p><p>An internal link connects pages on the same website. It distributes link equity, helps crawlers discover and prioritise pages, defines content hierarchy and improves user experience by guiding navigation to related content. An effective internal linking architecture improves the indexing and ranking of key pages.</p><p><h2 id="h2-44-pillar-page">Pillar Page</h2></p><p>A pillar page (or cornerstone content) is a comprehensive page that covers a broad topic exhaustively and links to cluster pages (topic clusters) that go deeper on specific sub-topics. The pillar-cluster model signals to search engines the site's topical authority on a given subject.</p><p><h2 id="h2-45-topic-cluster">Topic Cluster</h2></p><p>A topic cluster is a group of thematically related pages built around a central pillar page. Cluster pages cover specific aspects of the topic and interlink with each other and with the pillar page. The model helps Google understand the depth of a site's coverage of a topic.</p><p><h2 id="h2-46-open-graph">Open Graph</h2></p><p>The Open Graph protocol (og:) defines HTML meta tags that control how a URL is displayed when shared on social media (title, description, image, type). Not a direct SEO ranking signal, but it influences CTR and shareability on social channels, which in turn can generate traffic and backlinks.</p><p><h2 id="h2-47-search-console-google-search-console">Search Console (Google Search Console)</h2></p><p>Google Search Console is a free Google tool providing data on a site's organic performance (queries, clicks, impressions, CTR, average position), reporting on indexing issues, crawl errors, manual actions and sitelink status. It is the primary SEO monitoring tool on the Google side.</p><p><h2 id="h2-48-pagerank">PageRank</h2></p><p>PageRank is Google's original algorithm that assessed the importance of a web page based on the quantity and quality of inbound links. The visible PageRank (toolbar PageRank) was discontinued in 2016, but the concept of link equity continues to influence Google's internal ranking. Domain Authority and Page Authority are third-party proxies approximating this concept.</p><p><h2 id="h2-49-organic-traffic">Organic Traffic</h2></p><p>Organic traffic is traffic from non-paid search engine results. It is distinct from paid traffic (PPC), direct (typed), referral (from other sites), social (from social media) and email. Sustainable organic traffic growth through SEO is a long-term strategy with decreasing marginal costs.</p><p><h2 id="h2-50-crawl-depth">Crawl Depth</h2></p><p>Crawl depth indicates the number of clicks needed to reach a page starting from the homepage. The deeper a page is in the site structure (many clicks from the home), the less frequently it will be crawled and the less link equity it will receive. Good site architecture keeps important pages within 3-4 levels of depth.</p>