Two nights; a period covering two nights, used in expressions like 'stay for two nights' or 'for two nights in a row'.
出張で二晩ホテルに泊まる予定だ。
I plan to stay at a hotel for two nights on my business trip.
彼は二晩連続で夜中まで仕事をしていた。
He worked until late two nights in a row.
祭りは二晩にわたって開催される。
The festival will be held over two nights.