a disc jockey (also known as dj or deejay) is a person who selects and plays recorded music for an audience.says wikipedia.
many modern djs add electronic effects to their dj sets relying on existing samples of other djs/music producers.
some djs produce their tracks live at the club.
and then there is beardyman, a beat box guru, who produces whole dj sets constructed live from his vocalisations only, using looping effects. he usually makes heavy use of korg's kaoss pads.
beardyman live looping @ lethargy (august 13th, beginning of the 2010 streetparade in zurich @ rote fabrik --- more on flickr):
disclaimer: don't record loud music using an iphone;-)
other beardyman performances
using the kaoss pads:
live show with improv beatboxing and looping:
beardyman is also really good at producing random sounds: