First, it is used to describe a High-low split game without a declaration. That is, in a cards speak game, players all reveal their hands at the showdown, and whoever has the highest hand wins the high half of the pot and whoever has the lowest hand wins the low half.
The other context is as a house rule in many casinos: on any showdown, the players need not announce the value of their hand, but merely show it. All players at the table, the house dealer, and floor persons are entitled (and expected) to read all exposed hands and award the pot appropriately. Furthermore, a player misreading his hand is not penalized if the error is pointed out to him. These are the common house rules for low-limit games in most casinos. It is important that this rule applies only to hands that are properly tabled, that is, laid face up for evaluation. Even in casinos with a cards speak policy, it is a serious breach of etiquette (and possible violation of the One player to a hand rule) to advise another player about the value of his hand before he has deliberately exposed it, since his decision whether to expose the hand or fold it must be made alone. But once any hand is tabled, that player no longer faces any game decisions, so all players can (and should) read all exposed hands.