what is a dud?

Answer #1

flop: someone who is unsuccessful misfire: an explosion that fails to occur turkey: an event that fails badly or is totally ineffectual; “the first experiment was a real turkey”; “the meeting was a dud as far as new business was concerned” failing to detonate; especially not charged with an active explosive; “he stepped on a dud mine”

Usually the first one.

Source: Google

Answer #2

Pwincess nailed it. I was going to say an explosive failure. It could be a marketing failure, too.