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Wiktionary
half rest

n. 1 (context music English) A pause or interval of silence equal in duration to two quarter rest or one half of a whole rest. In common or 4/4 time, its duration is two beat. 2 (context music English) 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.

WordNet
half rest

n. a musical rest having the time value of half a whole rest or equal in duration to two beats in common time