A loner is a person who spends a lot of time alone. Sometimes that is a choice: they like their own company, they do not need a big group, and they are fine eating or travelling by themselves. Sometimes the word is a little sadder: a loner has almost no friends and is left on the edge of the group. In everyday English it is not a very cruel word. It can even sound a bit cool, like someone who walks their own path. People say “he's a loner” or “I'm a bit of a loner,” more about habit than about one quiet afternoon. It is not the same as lonely. A lonely person wants company and does not have it. A loner may not want a crowd at all. Teachers and parents use it about students; films use it about the quiet character who does not join in.