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CAPTCHA - definition and synonyms


What are red words?

90% of the time, speakers of English use just 7,500 words in speech and writing. These words appear in red, and are graded with stars. One-star words are frequent, two-star words are more frequent, and three-star words are the most frequent.


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  1. From our crowdsourced Open Dictionary
    an acronym which describes a program that protects websites from spammers by providing a test (e.g. a distorted text) which humans can do but computers cannot. It stands for 'Completely Automated Public Turing Test To Tell Computers and Humans Apart' and is a trademark of Carnegie Mellon University. There are visual as well as audio captchas in use.

    Recognising the kinds of characters used in CAPTCHAs remains a significant challenge in computer vision.

    Submitted on 28/09/2009
quiz invitation


a description of an economic or political situation based on analysis of information at the present time

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an unregulated form of capitalism that features financial deregulation, privatisation and low tax for high earners

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A must for anyone with an interest in the changing face of language. The Macmillan Dictionary blog explores English as it is spoken around the world today.

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