Web crawlers, also known as web spiders or web bots, are automated programs that systematically browse the internet to index content for search engines like Google and Bing. They follow links from one page to another, gathering information about websites to help users find relevant content quickly. These crawlers play a crucial role in how search engines operate, as they collect data on various web pages, including text, images, and metadata. This information is then used to rank pages in search results, making it easier for users to discover the information they need online.