evening high school; night high school
A high school that holds classes in the evening or at night, often for working students.
He works during the day and attends evening high school.
定時制高校 is a part-time high school (often with daytime and evening courses), while 夜間高校 specifically refers to evening/night classes.
通信制高校 is a correspondence high school, where students study mainly at home, unlike 夜間高校 which requires in-person evening attendance.
Compound of 夜間 (やかん, 'nighttime') and 高校 (こうこう, 'high school').