What is search engine optimization?
Put simply, SEO is a set of principles, practices and processes meant to help search engines like Google, Bing, Baidu and DuckDuckGo easily discover, map and understand the content of a website in order to include it and rank it in its ever-growing database, so that users can find it when they type in certain keywords.
Search engines use hundreds of signals and ranking factors to determine which websites have done a good job in making their content easily discoverable and accessible to users; some of these are technical aspects, like the speed and accessibility of websites, others are what SEO professionals call on-page factors, such as making judicious use of HTML headings and page titles, and others are quality factors, like the quality, uniqueness and completenes of the website content.
Websites that comprehensively and adequately take into consideration the ranking factors and rules of the popular search engines tend to perform better.