Welcome to English in a Minute.
Sometimes, American English is confusing and hard to understand, like: burn the midnight oil.
Everybody knows Americans burn a lot of oil, but is there a special oil that they burn in the middle of the night?
A: I have big exam tomorrow.
B: Are you prepared?
A: No, not at all! I have to burn the midnight oil, I need to do well on this exam.
Americans are not burning a special oil reserved for the middle of the night, they are just staying up very late.
This actually makes sense if you think of a candle, or a lantern, and you have a lot of work to do, that may take you all night.
This is a phrase everybody will understand, and you can use this phrase when you have a lot of work to do, and not that much time to do it in.
And that's English in a Minute.