Commercial card game developed in 1971 by Merle Robbins from the playing card game Crazy Eights. It is currently marketed by Mattel.
In the game, players discard cards matching the color or number/symbol of the card on a discard pile. Certain action cards call the next color to play, reverse the direction of play, force the next player to draw a certain number of cards, or forfeit the next player's turn altogether. A player has to shout "Uno" (Spanish/Italian for "one") to warn other players they are down to their last card; a round ends when a player runs out of cards. Points are scored by adding values of the other players' cards and awarded to the player that ran out.
One popular house rule (not an official rule) is to counter a "Draw 2/4" card by playing a similar "Draw 2/4" card, thus "stacking" the number of cards the following player has to draw.
