CAPTCHA means Completely Automated Public Turing test to tell Computers and Humans Apart. It was first used in Carnegie Mellon University in the year 2000.
Why CAPTCHA is used
CAPTCHA is used to identify if some service is accessed by human or machine and it works on the principle that human being is more smart then machine and can only does certain type of talk i.e. identify the character from some wired pattern.
