A disc jockey (also known as DJ or deejay) is a person who selects and plays recorded music for an audience.

There are several types of disc jockeys. Radio DJs introduce and play music that is broadcast on AM, FM, shortwave, digital or online radio stations. Club DJs select and play music in a bar, club, disco, a rave, or even a stadium. Hip hop disc jockeys select, play and create music with multiple turntables, often to back up one or more MCs. In reggae, the disc jockey (deejay) is a vocalist who raps, toasts or chats over recorded rhythm tracks while the individual choosing and playing them is referred to as a selector. Mobile disc jockeys travel with portable sound systems and play at a variety of events.

Equipment and techniques

DJ equipment may consist of:

• Sound recordings in a DJs preferred medium (eg. vinyl records, compact discs, computer media files)
• A combination of two devices, or sometimes one if playback is digital, to play sound recordings, for alternating back and forth to create a continuous playback of music (e.g. record players, compact disc players, computer media players such as an MP3 player)
• A sound system for amplification or broadcasting of the recordings (e.g. portable audio system, PA system) or a radio broadcasting system.
• A DJ mixer, an electronic, usually two-four channel, mixer with a crossfader used to smoothly go from one song to another (using two or more playback devices)
• Headphones, used to listen to one recording while the other recording is being played to the audience, and
• Optionally, a microphone, so that the DJ can introduce songs and speak to the audience.

Other equipment could or can be added to the basic DJ set-up (above) providing unique sound manipulations. Such devices include, but are not limited to:

• Electronic effects units (delay, reverb, octave, equalizer, chorus, etc). Some club DJs use a suboctave effect which creates a very low bass sound and adds it to the mix.
• A computerised performance system, which can be used with timecode encoded vinyl/CD content to manipulate digital files on the computer in real time.
• Multi-stylus headshells, which allow a DJ to play different grooves of the same record at the same time.
• Special DJ digital controller hardware can manipulate digital files on a PC or laptop, by using midi signals
• Samplers, sequencers, electronic musical keyboards (synthesizers), or drum machines.

Several techniques are used by DJs as a means to better mix and blend recorded music. These techniques primarily include the cueing, equalization and audio mixing of two or more sound sources. The complexity and frequency of special techniques depends largely on the setting in which a DJ is working. Radio DJs are less likely to focus on music-mixing technique than club DJs, who rely on a smooth transition between songs using a range of techniques.