Facecam

A facecam is the small window of you in the corner while the main picture is something else. It exists because the reaction is what people come back for; the gameplay is available from anybody, and your face responding to it is not.

Placement is a real decision. A corner that covers the minimap, the chat or the code you are explaining costs the viewer more than the reaction gains, and it changes per game. Circular crops and chroma key cutouts are both common. Lighting your face separately from the screen glow is what separates a facecam that reads clearly from one that looks like a webcam in a dark room.