A power nap taken on a plane, bus or train where you use your knees as pillows.
Tori was so tired on the flight to New Orleans that she took a lap nap.
When a girl performs such great oral sex on a guy, that it relaxes the guy so much he takes a nap, while her head is still in his lap.
That girl gave me a lap dance at the bar. Then I took her home and she gave me a lap nap.