Captcha

Part of speech: noun

Definitions

1. A challenge-response test used on websites to determine whether the user is human or automated software, typically involving distorted text or images that must be recognized and entered correctly
2. A security mechanism designed to differentiate humans from bots by requiring users to interpret and input characters or solve puzzles that are difficult for machines but easy for people
3. An interactive code or puzzle presented online as a way to prevent unauthorized automated access by verifying human users through pattern recognition tasks or similar challenges

Etymology: The word began as a deliberate coinage rather than an old word that drifted. In 2000, a team of researchers at Carnegie Mellon University needed a name for a test that could tell people from software, and assembled it as a loose acronym for "completely automated public Turing test to tell computers and humans apart." The name is a puzzle in itself: the Turing test, named after Alan Turing, asks whether a machine can pass as human in conversation, and this invention turns that idea inside out by asking machines to be identified by the very tasks they fail. The acronym was written in capitals, and the lowercase form "captcha" is simply the same term without capitals, which is how most people now write it. Nothing about the word was inherited from older English; its parts were chosen to describe the job, so the name reads as a short explanation of what the test is meant to do.

Synonyms: human verification, challenge test, verification code, Turing test