half rest

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

• noun A rest having one half the value of a whole rest.

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

• noun music A half rest is a pause or interval of silence equal in duration to two quarter rests or one half of a whole rest. In common or 4/4 time, its duration is two beats.
• noun music A symbol used in musical notation drawn as a solid rectangle directly 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 having the time value of half a whole rest or equal in duration to two beats in common time