lap dance

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An erotic dance that a stripper performs while straddling a customer's lap.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A very erotic form of entertainment, typically at a men's club, where a naked or nearly-nude performer straddles a customer and moves in a rhythmic, sexual manner over his or her lap.
• verb To perform a lap dance.