A form of deep penetration. When you're stretched as you far as you can take him and he pulls out a little bit only to use his body weight to push back in, stroking your cervix in a way that causes tremors to run up your spine and copious amounts of fluid to flood your channel.
"I swear guys, he's the best I've ever had. I mean, I'm spinal tapped on a nightly basis. I've never been so spoiled in my life."
The ball sack tap is the deft movement of tapping one's hand, palm up, onto someone else's ball sack (with or without clothes on). This can be done by males, to reward one another for something well done.
This can be demonstrated in the movie SuperTroopers during the first meeting, when Mac gives a ball sack tap to the Rookie after he sings the song.