This is a device common in many film trailers, especially nowadays. When a joke is delivered or something funny happens (often in comedy trailers), the background music stops, as if to tell you "this is when you're supposed to laugh". The music may also slow down
or stop with a needle scratch
The Trope Namer
is from James Rolfe's "Top 10 Worst Movie Clichés"
, where this made number 3.
Related to Trailer Joke Decay
NOTE: Since the Comedic Pause is all too common in trailers, no examples should be given.