A search engine is designed to search for information on the World Wide Web by using a spider to index web pages and store them in a database. The search engine then uses algorithms to find matching documents for search queries and displays results according to relevance. SEO, or search engine optimization, is the process of improving the visibility of a website in un-paid search engine results. It involves on-page and off-page optimization techniques to increase search engine rankings and attract relevant traffic. Common metrics for measuring SEO success include increased keyword rankings, website traffic, and revenue.