Club activities at school; extracurricular club or team activities (often shortened to 'bukatsu').
中学ではサッカーの部活動に入った。
I joined the soccer club activities in junior high.
部活動は週に何回ありますか？
How many times a week do you have club activities?
今年は部活動で大会に出場する予定だ。
This year we plan to participate in a tournament with our club activities.