A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a type of challenge-response test used to ensure that the response is generated by a human being. It is designed to prevent automated bots from accessing certain parts of a website, such as submitting forms, creating accounts, or scraping data. CAPTCHAs often involve tasks that are easy for humans but difficult for bots, such as identifying distorted text, selecting images that match a given category, or solving simple puzzles. They are an essential security measure to protect websites from abuse and ensure that interactions are genuine. While effective at deterring bots, CAPTCHAs can also impact user experience, making it important to balance security and usability.