There are various conventional shots. These frame a person or an object at a certain size or intimacy. These are standardized and universally understood by relevant film crew members. The limits defining each shot are not exact and there are regional differences (USA, Europe) regarding their definition, not to mention when taking into account the personality of the filmic language of a Director or Cameraman (Cinematographer/DP). The important standard is its relation to the film's main theme: An establishing shot offers viewers an overview of the setting and an introduction to the scene, or shows the central person or object in total and in the context of the setting. All subsequent shots originate from this initial view. A Close-up Shot (CU) is a very intimate view where for example only the head and face of an actor is shown. See also Full Shot, Medium Shot, Extreme Close-up, Long shot and Extreme Long Shot.
In some professional references, a full-length view of a human subject is called a medium shot; in this terminology, a shot of the person from the knees up or the waist up is a close-up shot. In other texts, these partial views are called medium shots. (For example, in Europe a medium shot is framed from the waist up). It is mainly used for a scene when you can see what kind of expressions they are using.
Medium shots are relatively good in showing facial expressions but work well to show body language.
Depending where the characters are placed in the shot, a medium shot can also be used to represent importance and power.