When you delay something until a later time or date, that's a postponement. If a trial lawyer doesn't have all the information she needs, she may ask the judge for a postponement until the following week.
A postponement can also be called a deferral or a stay, and it means rescheduling something for later. You can request a postponement of your chemistry test, but there's no guarantee you'll get it. When a baseball game or tennis match gets rained out, the teams agree on a postponement, starting over at the earliest opportunity. Postponement has a Latin root, postponere, "put after, neglect, or postpone."