reddit

“He is referring to those squiggly, distorted images commonly
seen when registering for internet services such as free email
accounts or blogging sites. The user has to type the letters in the
image before proceeding. Captcha stands for Completely Automated
Public Turing test to tell Computers and Humans Apart. The idea is
that humans can read the letters, but computers cannot, thus
preventing automated scripts from registering.” source...