SEO (search engine optimization) is the set of practices that increase a site's visibility in unpaid search results: from technology (speed, indexability), through content matching real queries, to authority built with links.
SEO stands on three legs. Technical: the search engine must fetch and understand the site efficiently (structure, structured data, Core Web Vitals, mobile). Content: the site must answer the questions people actually type – hence keyword and intent work. Authority: links and mentions from credible sources act as recommendations.
SEO is a long game: results arrive in months, but – unlike ads – they don't vanish the day you stop paying.
In 2026 SEO has a new front: AI search engines (ChatGPT, Perplexity, AI Overviews), which don't show a list of links but cite sources. Optimising for them is described under AEO and GEO.