Your lap is the top of your thighs when you sit down, where your cat might sit. Lap can also refer to a trip around a racetrack, or to the act of overtaking a competitor by a lap. Lap is associated with a number of idioms. If something "falls into your lap," you have gotten something without making much effort.
Tom: *Sits down*
Sarah: *Sits Down on Toms lap*
Tom: What are you doing, it's no nut november!
Sarah: I'm just making it harder for you. It's also "Sit on lap november".