Possibly the single most popular shot in film or TV, this is a shot of two characters, framing their head and torso. The bottom of the frame cuts off the characters somewhere around the waist. Along with the Over the Shoulder shot, it is one component of the Over Over Two Shot.

A classic Medium Two-Shot by director Raoul Walsh from his 1935 film Under Pressure.
Examples of Medium Two-Shot include:

Film -- Live Action