The original meaning of cold deck is that of fixing a deck with the intent of cheating. For example, a player might arrange with the dealer for a victim player to have a strong hand so that he bets a lot of money, but for another player (or himself) to have an even stronger hand.
It can also mean that the deck is stacked against a player so that he loses all his money over a long period of time.
The term is also used to describe a round of play in which stronger hands than usual are dealt. In Texas Hold'em, for example, if three players get a pair of aces, a pair of kings, and a pair of queens and then the third player hits a third queen, then you could say the deck is cold. As in the first meaning, it can also mean that over a long time, many situations occur where one player has a strong hand while another has a stronger hand still.