noun
tiered classroom; lecture hall
A classroom or lecture hall with stepped, tiered seating, common in universities.
大学の階段教室で講義を受ける。
I attend a lecture in the university's tiered classroom.
講堂 is a general auditorium or hall, while 階段教室 specifically refers to a classroom with tiered seating.
Compound of 階段 (stairs, steps) and 教室 (classroom), literally 'staircase classroom'.