Man-in-the-middle attack is a specific kind of cryptographic attack.
Wiki:
In cryptography and computer security, a man-in-the-middle, monster-in-the-middle, machine-in-the-middle, monkey-in-the-middle or person-in-the-middle attack is a cyberattack where the attacker secretly relays and possibly alters the communications between two parties who believe that they are directly communicating with each other.
Norton:
A man-in-the-middle attack is like eavesdropping. When data is sent between a computer and a server, a cybercriminal can get in between and spy. A man-in-the-middle attack requires three players: the victim, the entity with which the victim is trying to communicate, and the "man in the middle" who's intercepting the victim's communications.