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. Its popularity coincided with the rapid changes in recording technology in the 1950s and 1960s. 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 in 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 (and their airplay on the radio). Tape recording had become perfected, allowing artists more freedom as they composed songs, especially novelty songs. By the late 1980s and the early 1990s, the 45 rpm record would decrease in popularity and other means would be used to evaluate the popularity of new songs, such as cassette-single, CD single, and digital MP3/AAC sales (plus radio airplay).