辩论会 is the formal event — a structured debate with two sides (
正方 zhèngfāng /
反方 fǎnfāng), a moderator, and a clock. Distinguish from
辩论 biànlùn (the verb 'to debate' or general noun 'debate') and
讨论会 tǎolùnhuì (a discussion / panel, no adversarial sides).
会 (assembly) is the event-suffix.