The term, cold deck (when used as a noun), refers to a "stacked" deck (i.e., a deck of playing cards arranged in a preset order, to effect a specific outcome, once dealt) which is deceptively switched with the original deck of cards in play -- to the benefit of the player/dealer making the switch. The term refers to the fact that the cards in the stacked deck often are literally colder (to the touch) than those of the original deck (as constant handling of playing cards over several consecutive "hand"s warms them, due to transfer of body heat from the fingers to the cards).
In the broader sense, the term can refer to the preset deck itself, or, to the practice of using one (e.g., "I tried a cold deck on him but he spotted it in a second"). As a verb, the phrase can refer to cheating with, or being cheated by, use of a cold deck (e.g, "I think I may have been cold-decked when I lost that $800 pot)."
More recently, the term has come to refer to a hand that plays out as if a cold deck had been in use -- whether or not it actually was. For example, in most forms of poker, a legitimate four of a kind (i.e., four cards of identical rank, regardless of suit [e.g., "four Kings"]) occurs rarely; and, a straight flush (i.e., five cards of the same suit in consecutive face value [e.g., "the six, seven, eight, nine and ten of spades"]) is rarer, still. If one player is dealt four-of-a-kind and another is dealt a straight flush, both players would usually be justified in making large bets and raises. If/when the player with the straight flush wins the pot, the player dealt the four-of-a-kind might only jokingly complain of having been cold-decked. The hand itself is called a "cooler".
In card magic
Magicians use prearranged decks of cards to perform some effects. This can range from a deck that is completely arranged in a known order (for example, the Si Stebbins arrangement) to one in which a few cards have been placed in particular locations. The use of a cold deck necessitates some form of false shuffle and/or false cut to create the illusion that the cards are not prearranged. When only a few cards are prearranged, and these are together, those cards are often referred to as the "stock" by magicians.