Dud

Not an actual card type in itself, 'dud' is simply the name given to cards that are of no use to a given side. These are:

Crew

 * Chestburster
 * Alien
 * The Robot (once the Character has been revealed to be the Robot)
 * Alien Interrupts

Alien
Dud cards should generally be discarded during the discard phase of your turn, to make room in your hand for something better. There may be occasions, however, when you might legitimately choose to keep dud cards in your hand.
 * Chestburster (after being revealed as a decoy Mystery Marker)
 * The 'Robot' (once it has been destroyed)
 * Crew Interrupts