Short answer: SEO is everything you do to improve your visibility in Google without paying per click.
Google uses an algorithm to determine which pages provide the best answer to a user’s search query. Those pages appear at the top. SEO is the work involved in making your page that answer: the technical foundation of the site, the structure of your pages, the content itself, and the extent to which other sites link to you.
What it is not: a trick or a button. There is no setting you simply turn on. It is a series of small improvements that collectively make a difference, and which you must continue to maintain because your competitors are doing the same.
Since AI assistants have begun summarizing answers, a second dimension has emerged. Being mentioned in ChatGPT or in a Google AI overview requires the same foundation, but with more emphasis on factual, well-structured content that is easy to cite. This is called GEO, and in practice, it evolves alongside SEO.
Do not expect results within a few weeks. The first improvements are usually visible after six to eight weeks, while structural growth is built over three to six months.