A disc jockey (also known as disk jockey, DJ or deejay) is someone whose job is to select and play recorded music tracks for the enjoyement of an audience (he do not therefore creates it). Initially, the disk (disc) is a phonograph record while the disc that we know today refers to the Compact Disc, the most common spelling is thus "disc".

There are several types of disc jockeys. The radio DJs (or resident DJs) have to present the music that is broadcast on AM, FM, shortwave, digital, or on the Internet radio stations.
Discos DJs have to select and mix the music in bars, nightclubs, discotheques, at raves, or even in stadium on particular events.
Hip-hop DJs have to select and play music using multiple turntables, often to backup one or more tracks. They can also "scratch" on the turntable to create percussive sounds.
In reggae, DJs are rap singers who, "toast" (speak or sing as part of a time on a monotonous melody) on pre-recorded tracks. However the person responsible for selecting and playing music is called a selector. Mobile DJs (non-resident, such as David Guetta, for example) moving around the world (for the most famous of them) with their portable sound system and play recorded music at various events.

The selecting and playing recorded music for an intended audience part of deejaying is the same for every disc jockey. Such elements as the selected music, the audience, the setting, the preferred medium, and the level of sophistication of sound manipulation are factors that differentiate the various DJ types.