Idiom of the Day from long ago when people still used candles for light. If you “burn the midnight oil,” this means you are going to work all throughout the night to get a task done. Maybe there is a very important deadline due the next morning and you need to spend a lot of time on it before it is completed. Rather than sleep, you instead work on this important matter until it is finished. You will be “burning the midnight oil” by keeping the lights on all night to keep working - and probably to help you stay awake.
“Burn the midnight oil”
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