Alt Text
Alt text, short for alternative text, is a written description of an image added in a page's code so that the meaning of the image is available when the image itself is not. It is read aloud by screen readers to people who are blind or have low vision, shown in place of an image that fails to load, and used by search engines to understand what an image depicts. Its first purpose is accessibility, making visual content usable by everyone, and a well-written description happens to help image search and on-page SEO at the same time because it communicates meaning rather than appearance.
Backlinks
A backlink is a link from one website to a page on another website. Search engines treat backlinks as signals of trust and relevance, reading a link roughly as a vote that the linked page is credible or useful, which is why backlinks are one of the main ways sites earn authority and rank. Not all backlinks carry equal weight: a link from a relevant, respected site counts for far more than one from a low-quality or irrelevant source.
Canonical Tag
A canonical tag is a snippet of HTML, written as a link element with rel="canonical", that tells search engines which URL you consider the preferred, master version of a page when several URLs show the same or very similar content. It consolidates duplicate and near-duplicate pages onto one address so that ranking signals are gathered in a single place rather than split across variants.
Click-Through Rate (CTR)
Click-through rate (CTR) is the percentage of people who click a link out of everyone who saw it. It is calculated by dividing clicks by impressions and multiplying by one hundred, so a result shown 1,000 times that earns 50 clicks has a CTR of 5%. It is used across search results, paid ads and email to measure how compelling a listing or link is to the people who encounter it.
Conversion Rate Optimisation (CRO)
Conversion rate optimisation, usually shortened to CRO, is the practice of increasing the percentage of website visitors who take a desired action, such as making a purchase, submitting an enquiry or signing up. The conversion rate is that percentage, calculated by dividing the number of conversions by the number of visitors, so raising it means getting more value from the traffic you already have rather than simply buying more of it. Good CRO works by understanding why visitors do or do not act, then removing the friction and answering the doubts that stand between them and the decision, and confirming each change with evidence rather than assuming it helped.
Core Web Vitals
Core Web Vitals are three Google-defined metrics that measure real-world page experience: Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness) and Cumulative Layout Shift (visual stability). Together they gauge how fast, responsive and stable a page feels to the people using it.
Cumulative Layout Shift (CLS)
Cumulative Layout Shift (CLS) is a Core Web Vitals metric that measures how much the visible content of a page moves around unexpectedly as it loads. It scores the visual stability of a page: high CLS means elements jump as images, fonts or injected content load, often causing a visitor to tap the wrong thing. A good CLS is 0.1 or less, measured on real-world field data.
Digital PR
Digital PR is the practice of earning links, mentions and coverage from real publications by giving journalists something genuinely worth covering, such as original data, a clear position or a real story. It is the authority layer beneath SEO and AI search: the reason rankings hold and answer engines treat a brand as a credible source.
Domain Authority
Domain Authority (DA) is a third-party metric, created by the SEO software company Moz, that scores a website from 1 to 100 to predict how well it might rank in search results. It is not a metric Google uses and it is not a ranking factor; it is an estimate produced by an independent tool, based largely on a site's backlink profile, and is best used for rough comparison rather than treated as an official measure of a site's standing.
E-E-A-T
E-E-A-T stands for Experience, Expertise, Authoritativeness and Trust. It is the framework Google's Search Quality Rater Guidelines use to judge whether a page and the people behind it can be relied on, with Trust as the element the other three exist to support.
Google Tag Manager (GTM)
Google Tag Manager (GTM) is a free tag management system from Google that lets you add, edit and organise the tracking and marketing tags on a website from a single interface, without changing the site's code each time. A small container snippet is installed once, and from then on tags such as Google Analytics, conversion tracking and advertising pixels are configured and deployed through GTM rather than being hard-coded into the site.
Interaction to Next Paint (INP)
Interaction to Next Paint (INP) is a Core Web Vitals metric that measures how quickly a page responds visually after a user interacts with it, tapping, clicking or pressing a key. It captures the delay between the interaction and the next frame the browser paints, across all interactions in a visit, reporting close to the worst. A good INP is 200 milliseconds or less, measured on real-world field data. It replaced First Input Delay as a Core Web Vital in March 2024.
Knowledge Graph
A knowledge graph is a structured map of real-world things, called entities, and the relationships between them. Instead of storing loose keywords, it records that a specific person, place, company or concept exists, what type of thing it is, and how it connects to other entities, so that a machine can reason about meaning rather than just match text. Google's Knowledge Graph is the best-known example: it powers the information panels in search results and helps search engines and AI assistants understand that a query refers to a particular entity, distinguish it from others that share the same name, and pull in related facts.
Largest Contentful Paint (LCP)
Largest Contentful Paint (LCP) is a Core Web Vitals metric that measures how long it takes for the largest content element visible in the viewport, usually a hero image, heading or main block, to render after a page starts loading. It is Google's proxy for how quickly a page feels usefully loaded to a visitor. A good LCP is 2.5 seconds or less, measured on real-world field data rather than a lab test.
llms.txt
llms.txt is a proposed standard file, placed at the root of a website much like robots.txt, that offers large language models a curated, plain-text guide to a site's most important content. It is intended to help AI systems find and understand the pages that matter, expressed in clean Markdown, rather than having to infer that from cluttered HTML. It is an emerging convention rather than an established, universally adopted standard, and support for it is currently limited.
Meta Description
A meta description is a short piece of HTML that summarises the content of a web page. Search engines may show it as the snippet of text beneath the page's title in the results, so it acts as a brief advert for the page. It is not a direct ranking factor, but a clear, relevant meta description can influence how many people choose to click, which is why it is worth writing well.
PPC (Pay-Per-Click)
PPC, short for pay-per-click, is a model of online advertising in which you pay a fee each time someone clicks your ad, rather than paying for the ad to be shown. It is most associated with search advertising, where advertisers bid to appear against particular search queries and are charged only when a user clicks through, but the same pay-per-click model runs across shopping, display, video and social platforms. The appeal is that you buy visits rather than impressions, and the position of an ad is usually decided by a combination of how much you bid and how relevant and useful your ad and landing page are, not by bid alone.
ROAS (Return on Ad Spend)
ROAS, short for return on ad spend, is a marketing metric that measures how much revenue an advertising campaign earns for every pound spent on it. It is calculated by dividing the revenue attributed to the ads by the cost of those ads, and it is usually expressed as a ratio or a multiple, so a ROAS of 4 means four pounds of revenue for every one pound of ad spend. It tells you how efficiently your advertising turns budget into sales, but because it is based on revenue rather than profit, it is a measure of efficiency, not of whether a campaign actually makes money.
Schema markup
Schema markup is structured data added to a web page, usually as JSON-LD following the schema.org vocabulary, that states explicitly what the page and its contents are, so search engines and AI assistants can read the meaning of the page without having to infer it from the layout.
SEO (Search Engine Optimisation)
SEO, short for search engine optimisation, is the practice of improving a website so that it earns visibility in the unpaid results of search engines and, increasingly, in the answers given by AI assistants. It works across three connected areas: the technical foundation that lets a site be crawled, rendered and indexed; the content that matches what people are searching for and answers it well; and the authority, mainly links and citations, that signals a site can be trusted. Unlike paid advertising, the visibility SEO earns is not bought directly, which makes it slower to build but more durable, and it compounds over time rather than stopping the moment spending stops.
Technical SEO
Technical SEO is the practice of making a website easy for search engines and AI assistants to crawl, render, understand and index, so that its content is eligible to rank and be cited. It covers the underlying foundations, crawling, indexing, site architecture, rendering, page speed and structured data, rather than the words on the page or the links pointing to it.
Time to First Byte (TTFB)
Time to First Byte (TTFB) measures how long it takes for a browser to receive the first byte of a page from the server after requesting it. It captures the server response time, including any redirects, DNS lookup, connection setup and the time the server spends generating the page. TTFB is not itself a Core Web Vital, but it sets the ceiling on the others: a slow first byte delays everything that follows. A good TTFB is generally 800 milliseconds or less.
XML Sitemap
An XML sitemap is a machine-readable file that lists the URLs on a site you want search engines and AI crawlers to know about, so they can discover those pages and understand which ones matter. It is a discovery and prioritisation aid, not a ranking control: it tells a crawler where your important pages are and when they last changed, but it does not force anything to be crawled, indexed or ranked.
Zero-Click Search
A zero-click search is a search where the user gets their answer on the results page itself and never clicks through to a website. The answer is satisfied directly by the search engine, through features such as featured snippets, knowledge panels, instant answers and AI-generated overviews, so the query ends without a visit to any of the pages that supplied the information.