Captcha – Completely automated public Turing test to tell computers and humans apart
A test to determine whether a post is being made by a human or a bot. It normally has a question or questions that must be answered correctly such as the identification of obscured text in graphic form, or random questions that spambots are not usually currently programmed to answer correctly (eg “What 3-letter animal goes woof?”). A captcha test originally meant an obscured-text question, but is now widely used to mean any such test.