A hand undermined. In the following scenario, player X has AK, and player Y has QJ. The board is AQJ, giving a pair of aces to player X and two pair to Y, who leads. The last two cards to fall are 4,4. The board has counterfeited player Y's hand, and he loses. Player X has a higher two-pair! AA 44, compared to QQ JJ. See up. Easy to miss -- either that your two pair has been counterfeited, or that your single pair has been strengthened.
When one or more cards are rendered useless due to the nature of each game. E.g., if you hold A2 in Hold'em and the board reads A2454, then your 2 has been counterfeited due to the bigger board pair, making your final hand value AA445.