If a place, a job, or a group is male-dominated, most of the people in it are men, or men hold most of the power. We use it for work (a male-dominated industry), for sport, for politics, for a classroom — anywhere you look around and see that men run things, or that almost everyone there is a man. It does not mean men are better at the work. It only says how the group is filled and who is in charge. You will hear it a lot in news and in talk about fairness at work; it is a clear, modern phrase, a little careful but not stiff. Though actually, people sometimes stretch it: a field can still be called male-dominated even when a few famous women sit at the top, if the rest of the room is still mostly men.