What Is SEO? A Guide to Search Engine Optimisation

What is SEO, and what does search engine optimisation actually do?

SEO is all the work that helps a site appear more often, and for the right queries, in the free (organic) results of search engines. Its value is that it brings people who are searching for exactly what you offer, at that very moment, to your site without depending on an advertising budget.

The abbreviation comes from the English phrase Search Engine Optimization. Google’s SEO Starter Guide defines SEO as helping search engines understand your content and helping users find your site. In practice, it is technical and strategic work carried out in line with search engines’ guidelines (known at Google today as Search Essentials): the site’s infrastructure, the content of its pages and the site’s reputation across the web are all handled together.

What SEO brings a business can be grouped under five headings.

• Visibility at the moment of demand: You appear in front of the person searching for your product or service right then, and unlike advertising, you don’t pay separately for clicks.
• Compounding traffic: A well-built page can keep bringing in visitors for a long time, as long as it stays live and up to date; in this respect it differs from traffic that fades as soon as the ad budget is cut.
• Trust and awareness: Users start to recognise a brand they keep seeing in organic results, and that recognition also supports advertising, social media and sales conversations.
• A better website: Speed, mobile-friendliness, clear navigation and clear content serve both the search engine and the visitor, which is why SEO work can also contribute to your conversion rate.
• Eligibility for AI answers: Google features such as AI Overviews and AI Mode also draw on pages in the search index; according to Google, to be shown as a supporting link in these answers, a page must be indexed and eligible to be shown with a snippet.

Let’s also separate two concepts that are often confused. An organic result is a position earned without payment; Google does not accept payment to include a page in organic results or to rank it higher. SXO (search experience optimisation) is a term that emphasises the user-experience side of SEO, meaning that someone arriving from search quickly finds what they came for on the page; it is not the same thing as GEO, which describes visibility in AI answers.

How does Google find, index and rank a page?

Google processes a page in three stages: in crawling, Googlebot finds and downloads the page; in indexing, it analyses the content and stores it in its index; and in serving results, when someone searches, it ranks the pages in its index that are most relevant to the query. Every part of SEO exists to make one of these three stages easier.

This process has two important limits. First, Google does not guarantee that any page will be crawled, indexed or shown; meeting the technical requirements only makes a page eligible. Second, Google does not take payment to crawl a site more often or to rank it higher. That is why offers selling “Google registration” or “priority indexing” deserve a healthy dose of scepticism.

In our audits, some of what looks like a ranking problem actually starts in the first two stages: a noindex tag left behind from the test environment, a wrong canonical URL, or product pages that receive no links from any other page. That is why we start every site by confirming that it can be crawled and indexed, before we touch the content. We cover search engines other than Google, and how they work in general, in a separate guide to search engines.

What are the main types of SEO? Technical, on-page and off-page SEO

SEO falls into three main areas: technical SEO, which keeps the site crawlable, fast and secure; on-page SEO, which shapes a page’s content and tags around search intent; and off-page SEO, which strengthens the site’s reputation and links across the web. None of the three can stand in for the others; the weakest link limits the impact of the other two. SEO is itself one channel that works alongside other areas of digital marketing such as social media, websites and software.

Technical SEO

Technical SEO is the infrastructure work that lets search engines crawl and process a site without problems and lets visitors use its pages quickly and securely. robots.txt and sitemaps, redirects and status codes, canonical tags, HTTPS, mobile-friendliness, Core Web Vitals and structured data all fall under this heading. We share a detailed checklist in our guide to what technical SEO is.

On-page SEO

On-page SEO makes sure each page gives a clear answer to a single search intent. Keyword and intent research, the title tag and meta description, heading hierarchy, descriptive URLs, image alt text and file size, internal links and the content itself are all handled here. The goal is not to repeat the keyword but to answer the searcher’s question in full; the practical steps are covered in our on-page SEO guide.

Off-page SEO

Off-page SEO is everything that happens outside your site and affects how trustworthy you are. Its best-known part is the backlink, a link from another site to yours: natural links from reputable, relevant sites in your field help Google understand pages and the relationships between them. Google states that PageRank, which evaluates links, has been one of its core ranking systems since the very beginning and is still part of those systems; even so, ranking is carried out by systems that look at many factors besides links. Digital PR, news coverage that mentions the brand, industry lists and customer reviews also fall under this heading; we go into the details in our article on off-page SEO.

Measurement and specialist applications

Measurement is what holds the three areas together. Search Console shows which queries you appear for and which pages are indexed, while Google Analytics 4 shows how many of those visits turn into a form submission, a call or a sale; third-party tools such as Semrush, Ahrefs and Moz speed up competitor and link analysis. We compare which tool does what in our article on SEO tools. For businesses that serve customers at a physical address or in a defined area, local SEO is a distinct application of this framework, and for new sites, so is building SEO in while the website is being designed.

What does Google look for in 2026? Helpful content, E-E-A-T and page experience

In 2026 Google is still asking the same question: is this page genuinely helpful, trustworthy and useful for the person searching? It answers that not with a single signal but with core ranking systems that weigh up the helpfulness of the content, the reliability of the source, page experience and compliance with spam policies together.

Helpful content is no longer a separate system. The helpful content system, which originally ran on its own, became part of the core ranking systems in March 2024. So it is no longer accurate to talk about a separately running “helpful content update”; whether content was written for people or for search traffic is now part of every core assessment.

E-E-A-T is not a ranking factor but a quality framework. E-E-A-T, short for experience, expertise, authoritativeness and trustworthiness, comes from the guidelines Google writes for its quality raters. Google says E-E-A-T itself is not a specific ranking factor, but that using a mix of factors that can identify content with good E-E-A-T is useful. In practice, this means making it clear who the author and the organisation are, giving the content first-hand experience, backing claims with sources and keeping trust signals such as contact details visible.

Page experience has clear benchmarks. To count as “good” in Core Web Vitals, LCP must be 2.5 seconds or less, INP 200 milliseconds or less and CLS 0.1 or less; values are assessed at the 75th percentile of real-user data, separately for mobile and desktop. Because Google mainly uses the mobile version of a site for indexing, content and experience need to be complete on mobile first.

The official framework for what Google expects from a site is Google Search Essentials, which has three parts.

This framework is what Google’s “Webmaster Guidelines”, published under that name since 2002, became when they were simplified and renamed on October 13, 2022. The scope of the spam policies has also widened over time: the policies announced in March 2024 added scaled content abuse, expired domain abuse and site reputation abuse (today called the site reputation policy) to the list. Sites that violate the policies may rank lower, drop out of the results entirely or receive a manual action; we explain which methods fall within this scope in our article on black hat SEO.

AI summaries run on the same foundation. Google states that features such as AI Overviews and AI Mode rely on its core ranking and quality systems and that no special optimisation is needed to appear in them; according to its current guidance, optimising for generative AI search is still SEO as far as Google is concerned. We cover how these features choose their sources in AI Overviews and AI Mode, and visibility in other engines such as ChatGPT and Perplexity in what is GEO.

Google recalibrates these systems with core updates several times a year. The updates do not target specific sites, but they can shift a site’s visibility in either direction; we explain how we track them in our article on Google algorithm updates.

Which businesses should prioritise SEO, and which shouldn’t?

SEO is a priority for businesses whose product or service has steady search demand on Google and whose customers research before they decide. If search demand hasn’t formed yet, if results are needed within a few weeks or if customers come entirely through referrals, SEO still matters but may not be the first channel to invest in.

Rather than the blanket claim that “every site should do SEO”, we suggest starting with one question: are your customers searching for you or your competitors on Google? If the answer is yes, missing out on your share of that demand is business lost directly. The table below summarises the relative priority of SEO in situations we come across often.

A low priority doesn’t mean a site can ignore search engines. Every business needs to show up with accurate information when people search for its brand name, and to have a crawlable site; that is basic housekeeping that doesn’t require a large budget.

In e-commerce, on the other hand, SEO is usually not an option but part of the revenue plan: product and category searches create demand that keeps renewing itself. When traffic is needed in the short term, paid search steps in; we explain why Google ads don’t affect organic rankings, and how to plan the two channels together, in our article on the difference between SEO and SEM.

Where should you start with SEO?

SEO starts with measuring where the site stands today: verify Search Console, check that the site can be crawled and indexed, and identify which queries you already appear for and which pages bring in business. Goals and priorities are set once you have this data.

On most sites, the first few months follow roughly this order.

1. Set up measurement: Verify a Domain property in Search Console and define key events such as form submissions or sales in Google Analytics 4.
2. Clear technical blockers: Use the Page indexing report to check whether important pages are indexed, and look for robots.txt and noindex errors.
3. Map the demand: List the searches your customers use and match each one to the single page that best meets its intent.
4. Take the closest opportunity first: Improving pages that already get impressions but sit on page two usually pays off sooner than writing new pages from scratch.
5. Put the plan in writing: Draw up a roadmap that ranks technical, content and authority work by impact and effort, and measure it every month.

We walk through each of these steps in practice in our guide to how to do SEO, and explain our prioritisation method in our article on SEO strategy. The mistakes that waste the most time when getting started are collected in our article on common SEO mistakes.

It pays to be realistic about timing: the effect of some technical fixes can show up as Google recrawls the page, while lasting progress on competitive searches can take months. We look in detail at the factors that determine the timeline in our article on how long SEO takes to deliver results.

If you’d like to see where your site stands within this framework, you can start with a free SEO and GEO analysis. The monthly scope of technical, on-page and off-page work is set out item by item in our SEO packages, and we report on every month.