whole rest

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

• noun A rest having the value of four beats in common time.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun music A whole rest is a pause or interval of silence equal in duration to two half rests or one half of a breve rest. In common or 4/4 time, its duration is four beats.
• noun music A symbol used in musical notation drawn as a solid rectangle directly below the line above the middle line of a staff whose height is half the distance between lines.

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

• noun a musical rest equal in duration to four beats in common time