A portrait could be more simple and more complex, more obvious and more profound. Humans are social creatures. We love to reflect on ourselves and the people we cherish, and we like to have that ability whenever we please. It shows a subject appearance, identity, mood and soul. It gives details such as clothing, hairstyle, facial expressions, and body language to teach us about a subject.
Portraits are about people, where your camera is pointed at and what you are trying to influence a perception of them, or could be what you feel about them.