One night; the duration of a single evening/night. Often used to say something happens or is completed within one night.
彼女は一晩で宿題を全部終わらせた。
She finished all her homework in one night.
その映画は一晩中上映されているわけではない。
That movie is not being screened all night long.
試験前は一晩勉強するつもりだ。
I plan to study for one night before the exam.
All night; overnight — throughout the night (without stopping).
昨夜は一晩中雨が降り続いた。
It rained all night last night.
赤ん坊が一晩中泣いて眠れなかった。
The baby cried all night and I couldn't sleep.
友達と一晩語り明かした。
I talked with my friend all night long.