A lap dance (or contact dance) is a type of erotic dance performance offered in some strip clubs in which the dancer typically has body contact with a seated patron. Lap dancing is different from table dancing, in which the dancer is close to a seated patron, but without body contact. With lap dancing, the dancer may be nude, topless or scantily dressed, depending on the laws of the jurisdiction and the club's policies. With full-contact lap dances, the stripper may engage in non-penetrative sexual contact with the patron, such as "grinding" his or her body against the patron. Variant terms include couch dance, which is a lap dance where the customer is seated on a couch. In some places, a "block session" of lap dances (usually a half an hour to an hour) can be booked in a "champagne room", which is a private room usually located in the back of a club. In many clubs, the duration of a lap dance is measured by the length of the song being played by the club's DJ. Charges for lap dances vary significantly.