Search engine optimization (SEO) involves strategies to increase website traffic by improving rankings in search engine results pages. There are two types of SEO - on-page optimization within the website like optimizing content and metadata, and off-page optimization like link building. Search engines index website content to include in their databases and rank pages using algorithms when users search. An effective SEO strategy includes keyword research, identifying target phrases, optimizing website code and content for keywords, obtaining quality backlinks, adding new content, and monitoring rankings and traffic.