Although MITM attacks are not exclusive to wireless, wireless technologies are prone to such attacks, because the adversary can perform them from a safe distance without having to worry about cabling and physical security.
MITM is an attack where the attacker relays and possibly alters the communication between two parties who believe they are directly communicating with each other. Spoofing allows us to impersonate hosts on the network through various methods, making those hosts send the traffic to our machine, rather than to the actual destination.