Also a radio format, once upon a time; the mother of all popradioformats. Featured fast-talking big-voiced echo-chambered DJs, annoying jingles (usually sung in fancy jazz harmonies), and a continuous rotation of a suit-defined (or gangster-defined) list of hits - often less than the proverbial (Billboard-defined) forty. In the 60's, freeform radio loosened Top 40's grip on American listening habits, before becoming infested with "consultants", who made FM "Top 40 2.0".