The period from evening to late night; night. Can also be used adverbially (e.g. 'at night').
夜は静かになるので、勉強に集中できます。
It becomes quiet at night, so I can concentrate on studying.
彼は夜遅くまで働いて、朝に帰ってくる。
He works late into the night and comes home in the morning.
夜、窓の外を見たら星がきれいだった。
When I looked out the window at night, the stars were beautiful.
Dinner; the evening meal (colloquial usage in some contexts or dialects).
今日は夜は家で食べる予定です。
Tonight I'm planning to eat at home.
忙しくて夜を抜くことが多い。
I'm often so busy that I skip dinner.
夜は七時に食べることにしている。
I make a point of eating dinner at 7:00.