A portrait is a portrayal of a person, usually showing the person's face (but not always). A portrait can be a painting, a photograph, an ink drawing, a sculpture — or even a description in words or in a film.
Portrait is a term often used when talking about artwork. Go to an art museum, especially one that has a historic collection, and you'll likely see many portraits hanging on the walls. Formal portraits were commissioned by wealthy people throughout history. A portrait can also be a written description of someone's appearance or character. If you describe your Mom in such detail that everyone can imagine what she's like, you've created a portrait of her.