What does Captcha [ C.A.P.T.C.H.A ] stand for ? Captcha stands for: Completely Automated Public Turing test to tell Computers and Humans Apart. It is used by many websites to make it harder for automated bots to download information from them. This bots are usually made by hackers and so many websites use this technology to counter them. it's not always successful because the bots are getting more sophisticated.