Definition of de-tacker
De-tacking means taking an opponent's entire stack. In other words, taking a player's entire stack in one move. If you are all in against a player who is evenly matched and you win the pot (and in turn, his stack), you are said to have de-tacked that player. We can also talk about disabling your opponent. For example, if you have AA and your opponent has KK on A-A-K-K-2, it is likely that your opponent will be destacked.
Use of the term de-tacker
As a general rule, in cash games where you are playing for money, you are more likely to talk about a flop, so if a player loses all his money, you are more likely to use the term de-tacker ("he got de-tacked"). The term de-tacker will be used more often in tournaments where you are building a stack rather than a stack. It's all a matter of convention, but you'll hear stack in tournaments and stack in cash games more often.