semibreve rest

Wiktionary

1. n. music A semibreve 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.
2. n. 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.