The Fidelipac, commonly known as a "NAB cartridge" or simply "cart", is a magnetic tape sound recording format used for radio broadcasting for playback of material over the air including radio commercials, jingles, station identifications, and music as well as for indoor background music. Fidelipac is the official name of the industry standard audio tape cartridge.

Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magnetic tape could with relative ease record and playback audio, visual, and binary computer data.