A disc jockey, (usually called by the initialism "DJ", or "deejay"), is an individual who selects and plays pre-recorded music for the enjoyment of others.
DJs can be heard on the radio or at any number of social gatherings, among them weddings, nightclubs, art openings, warehouse parties, or high school dances. As a result there are many different types of DJ, each fitting into a particular niche defined by performance setting (broadcast booth or nightclub) and intended audience (jazz or hip hop fans). A DJ's performance style and the techniques they employ reflect these considerations. Wedding DJs play music but are often expected to act as a masters of ceremonies who introduce the bride and groom, lead dances, or invite guests to play games. A DJ at a rave would not be expected to do any of these things, but would be expected to introduce a greater technical element to their performance by manipulating the songs they play in order to maintain a given tempo and energy level. It can be said that DJing is not a single action but instead a series of actions whose makeup is predicated upon a number of situational factors and expectations. The examples of talk radio "shock jocks" like Howard Stern and Don Imus show that one need not play music to be considered a DJ by some audiences, though the title "on-air personality" might be more appropriate for them.
The DJ as Artist
A recent phenomenon in the musical community (but primarily within the sphere of popular music) is the assertion that some DJs are not simply "playing records" but are in fact creating new music out of the playback and mixing of the pre-recorded media. Fuelled mainly by the innovative mixing techniques that have come out of the hip hop and EDM scenes, and regarded as a musical extension of the literary cut-up technique, this growing attitude posits that such a DJ is not content simply to beatmatch two or three records and layer them over each other but that the end product should emerge as a new musical composition. To achieve this goal, such a DJ may employ such techniques as phrasing, sampling, scratching, the application of effects (e.g., delay, flange, etc.), and any other technique the DJ feels inclined to use. Examples of such DJs as "artists" adding musical or dramatic value include DJ Shadow, Coldcut and DJ Spooky. In effect they are developing an aural montage that may be spontaneous/improvised or carefully crafted. There are parallels in surrealism and the visual arts.
Disc vs Disk
The name "Disc jockey" developed in the era when the only sound recordings available were analogue disc records. For the reason it's disc jockey rather than disk jockey, see disk or disc. Disc is more often spelled "Disk" in the USA.