To burn the midnight oil is a common expression that we use in English to mean that we work late into the night.
The definition is: To work late into the night.
Examples: He has really been burning the midnight oil studying for his exams. He hasn't had a good night's sleep for weeks!
I have a report due tomorrow so I will be burning the midnight oil tonight. If I don't, I will fail the course.
Try to use this expression as often as possible so that it becomes part of your vocabulary.
Here's another English lesson for you to look at.
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