Captcha is a kind of security feature that distinguishes between a human and a bot. This prevents bots or automated softwares to make fake accounts.

Example:
Suppose you are trying to create an account on a website. Before you can proceed, the website presents you with a visual puzzle or a simple question to prove that you are a human and not a bot. The challenge might be to identify and click on all images with traffic signals/ cars/street signs, or to type in a series of distorted or jumbled letters and numbers.