The Top Forty or Top 40 is a music industry shorthand for the currently most-popular songs in a particular genre. When used without qualification, it typically refers to the best-selling or most frequently broadcast popular music songs of the previous week. Top 40 became the dominant radio format of the 1960s, 1970s, and 1980s.
The Top 40, or top forty, whether surveyed by a radio station or a publication, was a list of songs that shared only the common characteristic of being newly released. Its popularity coincided with the rapid changes in recording technology in the 1950s and 60s. In 1954, the recording industry agreed upon a standard recording format for higher fidelity music, so any new record player could play any new record. Also that year, new single records were released on 45 rpm records and the Top 40 thereafter became a survey of the popularity of these records. Tape recording had become perfected, allowing artists more freedom as they composed songs, especially novelty songs.