disc jockey (abbreviated DJ, D.J. or deejay) is a person who mixes recorded music as it is playing. Originally, the “disc” in “disc jockey” referred to gramophone records, but now “DJ” is used as an all-encompassing term to describe someone who mixes recorded music from any sources, including cassettes, CDs, or digital audio files on a CDJ or laptop. DJs typically perform for a live or broadcast audience, but DJs also create mixes that are recorded for later sale and distribution. DJs use equipment that can play at least two sources of recorded music simultaneously and mix them together. This allows the DJ to create seamless transitions between recordings and develop unique mixes of songs. Often, this involves aligning the beats of the music sources so their rhythms do not clash when they are played together. DJ equipment also allows the DJ to preview a source of recorded music in headphones before playing it for the audience. Previewing the music in headphones helps the DJ pick the next track they want to play and cue up the track to the desired starting location so it will mix well with the currently playing music. The title “DJ” is also commonly used by DJs in front of their real names or adopted pseudonyms or stage names as a title to denote their profession.
The practice of modern disc jockey mixing was preceded by radio personalities who introduced and played individual selections of recorded music on broadcast radio stations. Records were played over the radio as early as 1906, although this did not become common until the 1920s. Christopher Stone was the first radio DJ in the United Kingdom, having joined the BBC in 1927, he went on to Radio Luxembourg in 1934. His relaxed, conversational style set the tone for future radio presenting. The term “disc jockey” was said to have been coined by radio gossip commentator Walter Winchell in 1935 to describe radio announcer Martin Block, although the earliest known use of the phrase in print is not until 1941 in Variety Playing recorded music for dancing and parties rose with the mass marketing of home phonographs in the late 19th century, and Jimmy Savile is credited with hosting the first live DJ dance party in 1943. Savile is also credited as the first to present music in continuous play by using multiple turntables. In 1947, the Whiskey A Go-Go opened in Paris as the first discotheque. In the 1960s, Rudy Bozak began making the first DJ mixers, mixing consoles specialized for DJing. In 1974, Technics started making their SL-1200 turntable, which became the most popular turntable for DJs due to its high torque direct drive design. Hip hop DJs began using the Technics SL-1200s as musical instruments to manipulate records with turntablism techniques such as scratching and beat juggling rather than merely mixing records. Although Technics stopped producing the SL-1200 in 2010, they remain the most popular DJ turntable due to their high build quality and durability. In 1998, the first MP3 digital audio player was released, the Eiger Labs MPMan F10. Final Scratch debuted at the BE Developer Conference, marking the first digital DJ system to allow DJs control of MP3 files through special time-coded vinyl records or CDs. While it would take sometime for this novel concept to catch on with the “die hard Vinyl DJs”, This would soon become the first step in the new Digital DJ revolution. Manufacturers joined with computer DJing pioneers to offer professional endorsements, the first being Professor Jam (a.k.a. William P. Rader), who went on to develop the industry’s first dedicated computer DJ convention and learning program, the “CPS (Computerized Performance System) DJ Summit”, to help spread the word about the advantages of this emerging technology. In 2001, Pioneer DJ began producing the CDJ-1000 CD player, making the use of digital music recordings with traditional DJ techniques practical for the first time. As the 2000s progressed, laptop computers became more powerful and affordable. DJ software, specialized DJ sound cards, and DJ controllers were developed for DJs to use laptops as a source of music rather than turntables or CDJs. In the 2010s, like laptops before them, tablet computers and smartphones became more powerful & affordable. DJ software was written to run on these more portable devices instead of laptops, although laptops remain the more common type of computer for DJing.
Note: copy from Wikipedia