A similar symbol is the whole rest, which usually denotes a silence for the same duration. However, it is often used to denote a rest lasting a full bar, whether that bar lasts four beats or not - for example, it is often used to denote a full bar rest in 3/4 time. Whole rests are drawn as filled-in rectangles hanging under the second line from the top of the musical staff.
Figure 1. A whole note and a whole rest.
See also: half note, quarter note, eighth note, musical notation