A hand is said to be "counterfeited" when a card is dealt that nullifies a player's hand advantage. For instance, a player holds A 2 against an opponent holding A K on an A 10 2 board for the best hand of two pair. The turn card is then dealt and is a 10 which then "counterfeits" the A 2 player's advantage as the other player now also has two pair and a better kicker and as such holds the best hand.
Most often used inCommunityCard games, aCard appearing on the board that doesn'tChange the value of one's own hand, but that makes it much more likely for an opponent to tie or beat you, often because it duplicates what was previously a valuableCard in your hand. Also "duplicate".
A board card that duplicates a card in your hand that makes it less valuable. An example is if you have a 56 and the flop comes 7-8-9, so you have a straight. Now the final card is a 6 making your hand almost worthless.