by 
Muck is a term that refers to a pile of cards that have been removed from play. It is typically kept by the dealer in a face down position on the table, and it is used as a graveyard for hands that are no longer live. If a hand touches the muck, it is dead and cannot win. Therefore, it is important to understand the muck and how to handle it properly.
Generally, a poker hand is considered live until it makes contact with the muck. However, the muck is often fouled by other players and this can cause serious problems for the player. Some examples include dropping the cards on the floor, touching the muck with the heel of a hand, and revealing one or more of the hole cards to opponents. The dealer can also foul a hand in other ways, such as if it is in the middle of the muck or above the center of the table.
In most cases, a dealer will only reveal cards in the muck when they are suspicious of collusion or when there is a problem with the hand. Generally, it is considered unethical for a player to ask the dealer to reveal cards in the muck. However, a dealer can also accidentally reveal cards in the muck by grabbing them as they pass them from player to player or when they are putting them back into play.
Some dealers may even declare a hand dead if it comes in contact with the muck at all, regardless of whether or not the card was actually revealed. For this reason, it is a good idea for players to position their cards in front of the dealer and to avoid strewing them around the table.
Mucking a hand is often done by simply pushing it toward the muck pile using the heel of the hand. Some players use this technique to keep their cards hidden, while others do it because it allows them to easily move their cards away from the muck in case they want to call a raise. However, there are also other methods of mucking that are less effective, such as sliding the cards over to the dealer without calling a fold.
Mucking a hand is important to learn for any poker player, especially when they are in a tournament. A mistake made in this regard can cost a player a lot of money and is best avoided by learning what the rules are regarding the muck and when it is appropriate to muck a hand. Moreover, it is important to pay attention to the time limit on online poker games and in casino cardrooms so that you do not miss out on a possible winning hand because you were trying to muck too early.