SEO stands for Search Engine Optimization, which is the practice of increasing the quantity and quality of traffic to your website through organic search engine results.
Organic search traffic is specifically any unpaid traffic that comes from SERPs.
Search engines such as Google and Bing use bots to crawl pages on the web, going from site to site, collecting information about those pages and putting them in an index. Next, algorithms analyze pages in the index, taking into account hundreds of ranking factors or signals, to determine the order pages should appear in the search results for a given query.
The search algorithms are designed to show relevant, authoritative pages and provide users with an efficient search experience. Optimizing your site and content with these factors in mind can help your pages rank higher in the search results.
Search engine algorithms change frequently and SEO tactics evolve in response to those changes. So if someone is offering you SEO advice that doesn't feel quite right, check in with the specific topic page.