A plan that is executed in the night and usually involves some kind of scam. The first use of this word was when Jeezuz tricked God into showing his lack of wisdom concerning undefined jumbles of letters.
Jeezuz: Mendo, I trolled kamichan with my plaun
Mendo: Jeezuz, which Gawd?
Gawd: Jeezuz, no wonder the hoomans hanged ya