Requiremnts Doc

The requirements Document lays out in plain English what your software should do. The goals should be very specific, if possible. If they can't be specific, then part of your task is making them specific by understanding the problem area better or soliciting better input. If you still can't nail down the requirements, then it is best if you simply choose early on what the requirements you will work towards will be rather than having unclear goals.

Part of defining the requirements is having a clear understanding of what the Use Cases will be.