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