a silence added in to a skit or scene for comical purposes.
it comes from the silence of a dead fish. it may be silent, but there's something about a dead fish that's pretty fucking funny.
Cartman: I know it was just a dream, I know I didn't have an anal probe, and I know that I am no under alien control!
Cartman: I LOVE TO SING-A, ABOUT THE MOON-A AND THE JUNE-A AND THE SPRING-A, I LOVE TO SING-A