A concertgoer is a person who goes to concerts — the one in the seat, not the one on stage. Papers and reviews like the word because it names the audience as a type of person: young concertgoers, regular concertgoers, classical concertgoers. It can mean someone who goes often, or simply someone who is there for that night’s show. It is a plain, see-through compound, not slang and not especially formal. You will also see concert-goer with a hyphen; both spellings are used. It does not mean a musician, a fan who only listens at home, or someone who goes to a play (that person is a theatregoer). Though actually, a person can be a concertgoer without being a “fan” in the loud, poster-on-the-wall sense: plenty of quiet people go because they love the music.