SEO stands for search engine optimization. SEO is the process of making your site rank as high as possible. The higher your site ranks, the more visible your business is, and more traffic and sales your business is likely to generate.
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, taking into account hundreds of ranking factors or signals, to determine the order pages should appear in the search result for a given query.