noun
night school section; evening division
Refers to the organizational unit within a school that holds classes in the evening or at night, often for working students.
彼は昼間働いて、夜間部で勉強している。
He works during the day and studies in the evening division.
この大学には夜間部がありますか。
Does this university have a night school section?
定時制 is a formal term for 'part-time (school) system', often used in high school contexts, whereas 夜間部 is more common in university settings.
Compound of 夜間 (やかん, 'nighttime') and 部 (ぶ, 'division, department').