Referring to one card, the only card left in the deck that has not been exposed to the players. "He caught the case card to make his full house" would mean there was only one card left in the deck that could complete his hand.
The last available card of a certain description (typically a rank). The only way I can win is to catch the case king., meaning the only king remaining in the deck.
The last card of a particular rank, ex if the other 3 jacks are in the discards, and you get the last jack.
The last card of a particular type. E.g. a player buys a king after three have been shown. He has bought the case king.
The last card of a denomination or suit, when the rest have already been seen.
The last card remaining of a certain rank in the deck, e.g. On a flop of A J 4 where you hold 44, you would need to catch the ‘case' 4 to make four of a kind.
The last card of a particular rank when the other three are already out
the last remaining card of a particular rank. This is often used in the context of having a 'set' and requiring the last card to make quads.
The one card that can save your hand. For example, when you're looking for the case ace on the river to make four of a kind.
The only remaining card of a certain value remaining. Eg. Three aces are out so the one in the deck is the 'case' ace.
The last available card of a certain value or suit.
The last available card of a particular value or suit.