Late at night; the small hours when it is very late.
夜更けに電話が鳴って目が覚めた。
A phone call rang late at night and woke me up.
彼は夜更けまで仕事をしていた。
He was working until late at night.
夜更けの散歩は静かで気持ちがいい。
A walk late at night is quiet and pleasant.