What type of attack intercepts legitimate communication and forges a fictitious response to the sender?

Man in the middle attack (MITM)

Explanation:

This a term popular with hackers in computer and cybersecurity fields. The man in the middle attack describes a situation whereby there is an in-between in the perceived private conversation of two persons online. The middle man acts like an intermediary between these two, eavesdropping on each others conversation and controlling it while making it look as though they are having a private cyber conversation.