Etymology

The term disc jockey was first used to describe radio announcers who would introduce and play popular gramophone records. These records, also called discs by those in the industry, were jockeyed by the radio announcers, hence the name disc jockey, which was soon shortened to DJs or deejays.

Today, there are a number of factors, including the selected music, the intended audience, the performance setting, the preferred medium, and the development of sound manipulation, that have led to different types of disc jockeys. However, today there are many different kinds of 'DJs' and it does not always mean 'disc jockey' in the traditional sense; for example, turntablist DJs use actual 'discs' whilst radio DJs may use a number of sound sources including music files, CDs, jingles, and other pre-recorded media.

As of 2007, many club DJs have begun playing sets almost entirely on CDJs, on compact disc instead of using vinyl.

( Information Source: Wikipedia )