According to Wikepdia, a portrait is a painting, photograph, sculpture, or other artistic representation of a person, in which the face and its expression is predominant. The intent is to display the likeness, personality, and even the mood of the person. For this reason, in photography a portrait is generally not a snapshot, but a composed image of a person in a still position. A portrait often shows a person looking directly (not always) at the painter or photographer, in order to most successfully engage the subject with the viewer.
vary according to shooting time, studio set up, various locations and post production for required results.