A device for playing vinyl records and hence a piece of basic equipment for any DJ.

A turntable set up for DJing( also known as a deck) has a number of features that may distinguish it from a common home record player. Different decks may have extra gimmicks but the following are pretty standard:

speed selector - allows you to choose the base speed at which the record will play. (ie 33rpm or 45rpm)
start/stop switch - allows you to quickly start or stop the turntable.
pitch control - allows you to adjust the speed of the record up or down from the base speed. You need this so you can beatmatch
slipmat - reduces friction and allows you to stop or move the record independently of the turntable platter.
strobe - a little light that strobes against dots on the side of the platter. If your platter is spinning at exactly the current base speed then this will make these dots appear stationary, otherwise they will appear to be moving forwards or backwards. This can be used as a quick check on the functioning of your pitch control
cartridge - contains the stylus or needle. A model commonly used by DJs is the Stanton 500AL.
tonearm - the arm that holds the needle on the record. These usually have a great manner of adjustments that can be made such as anti-skidding and suspension adjustment.

Although Vestax decks are growing in popularity, by far the most popular turntable with DJs is the SL 1200 MK2 or SL 1210 made by Technics. These decks are very tough and extremely reliable. They are also the defacto industry standard so if you get a gig you can pretty much bet the venue will have a pair of 1200s. AFAIK the only difference between the 1200 and the 1210 is that the 1200 is silver whereas the 1210 is black.