Originally Posted by Dark Night
Completely Automated Public Turing test to tell Computers and Humans Apart
is what Wikipedia says, and what captcha.net say...
though other take exception to this since a turing test is a test given to humans to tell computers and himans apart.
the turing test is applied to chat bots for instance to determin if youre talking to a real person or just to a program.
thus other have sugested it actually stands for
Completely Automated Program to Tell Computers and Humans Apart.
also known as a reverse Turing test...
also they aren't infallible, and most bot makers have found ways to defeat them.