To work or study late into the night in order to finish something.
Using the reference
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To burn the midnight oil means to stay up very late working, studying, or preparing.
The phrase points to extra effort outside normal hours. It often suggests dedication, but it can also hint at strain, deadline pressure, or a habit of overwork.
People use this idiom for students, writers, engineers, analysts, and anyone pushing through late-night work. It fits both admiration and mild concern.
The phrase is close to pull an all-nighter, but burn the midnight oil does not require staying up the entire night.
The image comes from the time when late-night work literally required burning oil in lamps. That older material reality is what gives the idiom its durable visual force.
The phrase can romanticize unhealthy work habits if it is used without acknowledging exhaustion or burnout.