1. To fit snugly in(to something), creating an audible snap when doing so. These pieces snap in near the base of the machine to keep it stable while you use it. The webcam snaps in the holster, which you can mount anywhere you want around your computer.
2. To cause or force something to fit snugly in(to something else), creating an audible snap when doing so. In this usage, a noun or pronoun can be used between "snap" and "in." I just need to snap these wings in the fuselage, and my model airplane will be finished! The soldier snapped in the magazine began firing the machine gun at enemy troops.
See also: snap