dust cover

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A removable or hinged plastic cover used to protect a piece of equipment, such as a turntable or printer.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a removable plastic protective covering for a piece of equipment
• noun a paper jacket for a book; a jacket on which promotional information is usually printed
• noun a large piece of cloth used to cover furniture that is not in use for a long period