Overnight means happening in or throughout the night, or lasting the night.
Travel and overnight accommodation are included.
旅行及夜间住宿包括在内。
An overnight success or sensation happens very quickly and unexpectedly.
In 1970 he became an overnight success in America.
1970年他在美国一夜成名。
Overnight bags or clothes are ones that you take when you go and stay somewhere for one or two nights.
He realized he'd left his overnight bag at Mary's house.
他意识到自己把过夜包落在玛丽家里了。
If something happens overnight, it happens throughout the night or at some point during the night.
The decision was reached overnight.
这个决定是在夜里做出的。
You can say that something happens overnight when it happens very quickly and unexpectedly.
The rules are not going to change overnight.
这些规则不会说变就变。