Darth Vader
Darth Vader is a nickname for the two black fours, the four of clubs and the four of spades.
The simple explanation
Darth Vader is the hold'em hand of two black fours. The name refers to the dark side in Star Wars. It is a small pair, not a strong hand. Other pairs have their own jokes.
A closer look
A pair of fours is a small pair, but not a terrible one. If opponents show aggression, they often have a higher pair or two overcards, so the hand is typically played for set value. Against a raise, call only when the price is low compared with the stacks.
A practical example
A player is dealt 4♣ 4♠ and says, 'Darth Vader.'
Full explanation
Darth Vader is a nickname for the two black fours, the four of clubs and the four of spades.
Darth Vader is a nickname for the two black fours, the 4♣ and the 4♠. The name comes from the ‘dark force’ of Star Wars, and the dark color of the suits.
Two fours are not a good hand, but not a terrible one either. It is playable before the flop, especially if the price is small.
After the flop, the hand is usually a fold unless it makes a set or the board is very low. As with other nicknames, it is just a name for the cards and does not change how the hand should be played.