A whole rest is a musical symbol that indicates a silence lasting for four beats in a measure. It is represented by a rectangular shape hanging from the fourth line of the staff. Whole rests are commonly used in various musical compositions to create pauses or breaks in the music. In music notation, whole rests help musicians understand when to remain silent, allowing for better timing and rhythm. They are essential for maintaining the structure of a piece, ensuring that the performer knows when to play and when to rest, contributing to the overall flow of the music.