Curtain refers to a piece of fabric or other material that hangs down to cover a window, divide a room, or provide privacy.
In theater, curtain means the large piece of fabric that separates the stage from the audience.
The term "curtain" also refers to:
1. A metaphorical barrier or concealment ("iron curtain")
2. The end of a performance ("it's curtains for you")
3. A surgical drape used in medical operations