Defined: When a player calls a bet and a raise without having invested anything in the pot previously, they are said to be "cold calling".
Cold calling has a bad connotation because when done without serious understanding of the situation, it is often a leak in player's game.
Most raises indicate a premium hand, such as AA, AK, QQ. When players decide to cold call a raise, and they do so without having a premium hand as well, they set themselves up for a situation where they are "dominated".
Here's an example:
Player A raises from early position with AK. Actions folds around to Player B, who is in late position with KJ. Player B cold calls the raise.
Now, Player B has put himself in a position where he can lose a lot of money. When flops like K-7-4 come, Player B will be betting and calling with the worse hand.
Here is a video demonstrating the potential perils of Cold Calling . . .