Captchas

Part of speech: noun

Definitions

1. Challenges designed to differentiate humans from automated systems by requiring recognition and input of distorted letters or images; security measures to prevent unauthorized computer access or spam; tests used to verify user authenticity on websites
2. Visual or interactive puzzles intended to confirm that an entity interacting with a system is a human and not a bot; security precautions to avoid automated abuse of online services; mechanisms requiring users to perform tasks that are difficult for machines but easy for people
3. Tests where distorted text or images must be identified and entered correctly to prove human presence; tools employed to secure online forms and services from automated attacks; verification methods that demand user interaction difficult for software programs to simulate

Etymology: "Captchas" is the plural of "captcha," the name for the distorted-text or image puzzles websites use to tell human visitors from automated programs. The word is an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart," and it was coined in 2000 by a team at Carnegie Mellon University, including Luis von Ahn, who was then working on ways to make bots easier to spot online. The singular form is what most people use when speaking of one such test, and the plural simply counts several of them, as in the many "captchas" a person might solve while buying concert tickets. Because the acronym is pronounced as a single word, it has taken on the ordinary behavior of a regular noun, which is why it takes a plain "s" in the plural.

Synonyms: CAPTCHAs, human verification tests, challenge-response tests, security tests, Turing tests