Upper Receiver

In firearms terminology, the receiver is the part of a firearm that houses the operating parts. There are many types and styles of firearm receivers. A bolt action or semi-automatic firearm receiver usually contains the bolt carrier group, trigger group, and magazine port.

In most handguns, the receiver, or frame, holds the magazine well or rotary magazine as well as the trigger mechanism. It is sometimes called the body of the firearm, while in the context of handguns (revolvers and pistols), it is often called the frame.