A deadline is a date or time when something must be finished. At work and school, most projects have deadlines. If you don’t get your paper in by the deadline, you won’t get a good grade.
If you think missing a deadline and getting a low grade is bad, think about how this word came to be: It was a line that went around a prison and if a prisoner crossed it, he could be shot. Now that’s a deadline! A deadline sounds scary, and it does frighten a lot of people — if you don't get a paper in by the deadline, you could lose points or fail. But hey, you’ll live.