Rhythm is the arrangement of sounds and silences in time. Meter animates time in regular pulse groupings, called measures or bars, which in Western classical, popular, and traditional music often group notes in sets of two (e.g., 2/4 time), three (e.g., 3/4 time, also known as Waltz time, or 3/8 time), or four (e.g., 4/4 time).

Meters are made easier to hear because songs and pieces often (but not always) place an emphasis on the first beat of each grouping. Notable exceptions exist, such as the backbeat used in much Western pop and rock, in which a song that uses a measure that consists of four beats (called 4/4 time or common time) will have accents on beats two and four, which are typically performed by the drummer on the snare drum, a loud and distinctive-sounding percussion instrument. In pop and rock, the rhythm parts of a song are played by the rhythm section, which includes chord-playing instruments (e.g., electric guitar, acoustic guitar, piano, or other keyboard instruments), a bass instrument (typically electric bass or for some styles such as jazz and bluegrass, double bass) and a drum kit player.