Deadline (emphasis on "a") is the deadline for the delivery of work to the customer , and in a broader sense - the hour X, that is the time of the onset of an important event or the expiration of any ultimatum.
The word deadline in English means literally "dead line", that is, the line beyond which one who does not do his work can safely cut off the head.
The reality is that deadlines are set in advance, but to work systematically and assiduously, so that you can safely catch the deadline, no one wants. Therefore before the deadline there is the effect of storming, when the deadline is already on the nose, and nothing else has been done, not learned or built.
Deadline is in the list: Slang