SEO stands for Search Engine Optimization, which is used for increasing the ranking, quantity and quality of traffic to your website.You might think of a search engines, like, Google, Yahoo!, Bing, etc as a website you visit to type a question or search a query. On the basis of your query keywords, search engine replies with a long list of links to webpages as result that could potentially answer your question.
I came across this blog, https://www.incrementors.com/blog/seo-search-engine-optimization/ where you can read more about SEO, (just a 5mins read)