CAPTCHA
A challenge-response test used on websites to distinguish human users from automated bots.
A CAPTCHA↗ (Completely Automated Public Turing test to tell Computers and Humans Apart) is a challenge presented on a website, distorted text, image selection puzzles, or a simple checkbox, designed to be easy for a human to solve but difficult for an automated bot or script. It's a common gatekeeper on login forms, comment sections, and account registration pages.
CAPTCHAs exist because automated bots are used to create fake accounts en masse, scrape content, or attempt thousands of password guesses per minute. Modern versions increasingly rely on invisible behavioral analysis, like mouse movement patterns, rather than forcing every visitor to solve a visible puzzle.