Robots.txt is a simple text file placed at the root of a website to communicate with web crawlers and search engine bots. It specifies which pages or sections of the site should not be accessed or indexed by these automated agents. By setting rules within the robots.txt file, website owners can manage crawler traffic, protect sensitive information, and optimize how their content appears in search results. While it helps guide compliant bots, it does not guarantee complete privacy or security, as not all bots adhere to its directives.