CUPP is a Common User Passwords Profiler.
The most common form of authentication is the combination of a username and a password or passphrase. If both match values stored within a locally stored table, the user is authenticated for a connection. Password strength is a measure of the difficulty involved in guessing or breaking the password through cryptographic techniques or library-based automated testing of alternate values.
A weak password might be very short or only use alphanumberic characters, making decryption simple. A weak password can also be one that is easily guessed by someone profiling the user, such as a birthday, nickname, address, name of a pet or relative, or a common word such as God, love, money or password.
That is why CUPP was born, and it can be used in situations like legal penetration tests or forensic crime investigations.