A fixed or prescribed number of people (quota) — e.g., the official number of positions, students, or staff allowed.
この大学の留学生受け入れ定員は年間50名だ。
This university's quota for accepting international students is 50 per year.
募集定員を超えたため、追加の選考が行われた。
Because applications exceeded the recruitment quota, additional selection was conducted.
定員が決まっているので、早めに申し込んだ方がいい。
Since there is a fixed quota, it's better to apply early.
The capacity (number of people) that a vehicle or venue can hold — e.g., seating capacity.
このバスの定員は45人です。定員を超えて乗車しないでください。
This bus has a capacity of 45 people. Please do not board beyond the capacity.
会場の定員は500名なので、チケットは早めに購入した方が安心だ。
The venue capacity is 500 people, so it's safer to buy tickets early.
定員に達したため、入場を一時制限しています。
Admission is temporarily restricted because capacity has been reached.