Definition: A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a type of challenge-response test designed to determine whether a user is a human or an automated bot. Its primary purpose is to prevent automated software from engaging in abusive behaviors on websites.

Example: CAPTCHAs are commonly used on online forms, where users may be required to complete tasks such as identifying specific images from a grid or typing distorted text displayed in a box, thereby verifying their human identity before submission.