A search engine is a software program that searches the internet for web pages and other content that match specific keywords or phrases. Search engines are essential for finding information on the internet, and are used by millions of people every day. The most popular search engines include Google, Bing, and Yahoo. Search engines use complex algorithms to determine the relevance and quality of web pages, and use a variety of factors to rank results, including keyword usage, backlinks, and user behavior. Search engine optimization (SEO) is the process of optimizing a website to improve its ranking in search engine results pages. Effective SEO requires an understanding of how search engines work and how to optimize content for specific keywords and audiences.