Here is gpt3.5 response, which was actually expected:
A PPT (Probabilistic Polynomial Time) algorithm is a type of algorithm used in complexity theory and cryptography. A PPT algorithm is an algorithm that runs in polynomial time, with a small probability of error on a uniformly random input. Specifically, a PPT algorithm is an algorithm that can be run in time polynomial in the size of its input, and that outputs the correct result with probability at least 1/2 + ɛ, where ɛ is a small positive constant.
In cryptography, PPT algorithms are often used to model the behavior of efficient adversaries or attackers that have limited computational power. PPT algorithms are used to analyze the security of cryptographic schemes, such as encryption and digital signature schemes, under the assumption that attackers can only use PPT algorithms to break the security of the scheme. If a cryptographic scheme is secure against PPT attackers, it is considered to be computationally secure in practice.
In summary, a PPT algorithm is a type of algorithm that runs efficiently with a small probability of error, and is often used to model the behavior of efficient attackers in cryptography.