The robots.txt file is a simple text file used by websites to communicate with web crawlers and search engines. It tells these automated programs which parts of the site they are allowed to access and index. By specifying certain rules, website owners can control how their content appears in search results. This file is typically placed in the root directory of a website. For example, if your website is "example.com," the robots.txt file would be located at "example.com/robots.txt." Properly configuring this file can help improve a site's SEO and protect sensitive information from being indexed.