Anything sexual from getting laid to playing with your balls. Or an adjective for something cool or fun.
Just had sex: "I got some good nadplay last night!"
Girl loves playing with balls, of just fucking: "She gives awesome nadplay."
When you're going to mastrubate: "I feel like some personal nadplay."
Something cool, or you like a lot: "That's some serious nadplay!"
Something WICKED cool: "Fucking nadplay extreme!!!"