A whole rest is a musical symbol that indicates a complete measure of silence in a piece of music, regardless of the time signature (except for 4/2 time where a double whole rest is used). It looks like a small solid rectangle hanging from the fourth line of the musical staff and represents a silence lasting the duration of a whole note (usually four beats in common time).

Key points about the whole rest symbol:

• It signals a rest or pause where no notes are played or sounded for a full measure.

• The symbol is a rectangle suspended below the fourth staff line, distinct from the half rest, which sits on the third line.

• When used in any time signature (like 3/4 or 4/4), a whole rest means silence for the entire measure, even if that measure is shorter or different from four beats.

• It is also called a "semibreve rest" in British English.

• In notation, the whole rest essentially 'fills' the bar with silence and is visually different from other rests which represent shorter durations.

Thus, the whole rest is a critical notation symbol to indicate a measure-long silence in music, helping performers know when to pause for the full length of a measure. If desired, I can provide a description or illustration of the visual symbol.