The act of making your hands flat (like a high five) and inserting one hand in a chicks ass and the other in her pussy then proceeding to clap your hands together.
A thunder clap is when your girl goes down on your dick on last time and you nut. They call it the thunder clap for 2 reasons. 1. That's the sound her butt makes, 2. You pass out and see lightning strikes for 5 minutes
Guy 1: I just got thunder clapped
Guy 2: What was it like
Its when a woman is bouncing her ass of your dick and at the same time as you nut her booty cheeks clap on your dick. Its said that when that happens the male orgasm is so powerful you'll see thunder.