An avatar is a small picture, icon, or set of letters used to represent a person or another item. It is like a small portrait on a name badge: it helps you recognize who is who without taking much space.
For example, a chat list might show a person's photo beside their name. If no photo is available, the first letter of the person's name can serve as a simple stand-in.
Do not rely on the picture alone to identify someone. Show a name or another clear label too, and use an image description when the picture carries information a reader needs.