The term muck can be used in a couple of different ways in poker. As a noun, it describes the pile of discarded cards during a hand. As a verb, it describes the action by which players throw away their hand (i.e., fold).
One example of the use of “muck” in a sentence would be: John sends his card to the muck. This means that John folded his hand, adding his cards to the other discards, ending his participation in the pot.
In most live games, once cards touch the muck, they are considered dead. Up until that point, a player may be able to retrieve their hand, but once the dealer picks up the cards and adds them to the muck, those cards cannot go back unless some highly unusual situation occurs.
If you want to use muck as a verb, you can simply substitute the word “fold” with it. For example, you can say: I raised from the button to try and steal the blinds, but John made it 5x my raise from the small blind, and I mucked my hand without even thinking.