club activities; extracurricular activities
Refers to school-based club activities, often after school. Synonymous with the shorter 部活 (ぶかつ), which is more casual.
See also: 部活
Many students participate in club activities in high school.
Club activity time starts at 4 p.m. every day.
部活動 refers specifically to school club activities, while 課外活動 is the broader term covering any activity outside the curriculum, including volunteer work and community events.
部活動 specifically means school club activities, while 課外 is the broader term covering any activity or lesson outside the regular curriculum.
Compound of 部 (ぶ, 'club') + 活動 (かつどう, 'activity'). The exact historical derivation is straightforward; the word is a modern term for school club activities.