Full of people — no vacancies; used for crowded places like trains or venues (e.g., standing room only, sold out).
ラッシュアワーの電車はいつも満員で乗るのが大変だ。
Rush-hour trains are always packed, making it hard to get on.
コンサートは満員で、チケットはすでに売り切れていた。
The concert was full and tickets were already sold out.
駅で満員の車両を避けて次の電車を待った。
I avoided a crowded car at the station and waited for the next train.