Other forms: duds
Something that doesn't work the way it's supposed to is a dud. A bomb or firework that doesn't explode is one kind of dud. A bad blind date is another kind.
When a bomb fails to explode, it's a dud. A long-planned surprise party that fails miserably when the guest of honor doesn't show up is another kind of dud. You can also refer to a person as a dud, if they're an utter failure or a complete flop: "The lead actor was a total dud. He couldn't really sing or dance and he seemed nervous." In the 1800s, a dud was "a person in ragged clothing," from dudde, "cloak or mantle."