After a deck of cards is shuffled by the dealer, it is often given to a player other than the one who performed the shuffle for a procedure called a cut.
Procedure
The dealer completes their shuffle, and then sets the cards face-down on the table near the designated player. The player cuts the deck by removing a contiguous range of cards from the deck, and places them either on top or bottom of the remaining cards. The simplest form of the cut is done by taking, roughly, the top one-half of the cards, and placing them on the table. Either the player cutting or the dealer then completes the cut by placing the remaining bottom portion on top of the cards that have been cut off.
Once the cut is complete, the dealer then picks up the deck, straightens or "squares" it, then deals the cards.
Etiquette
The continuous section may also be taken from the middle of the deck, though in some settings this is considered poor etiquette or against the rules. Likewise, a cut involving a very small number of cards, such as taking only the top card as a cut, is not often acceptable. The same is true when a player takes more than one section of cards from the deck.
During informal card games, the dealer is typically not required to offer the cut, and even if offered, the designated player can decline the request. On the other hand, any player may specifically request to cut the cards before they are dealt. If a cut is requested by a player, it must be granted by the dealer.
In formal settings, such as during high-stakes casino or tournament settings, an offer to cut the deck is mandatory and the designated player must perform the cut.
Reasons
The practice of cutting is primarily a method of reducing the likelihood of someone cheating by manipulating the order of cards to gain advantage. Even if the dealer does not plan on cheating, cutting will prevent suspicions, thus many rules require it. Some players also consider the cut to be lucky.
Related articles
The term cutting is also used for a random selection procedure in which a player perform the first part of a cut (removing a group of cards from the top of a deck), then look at the value of the card on the bottom of that
portion, then replaces it. Another player then does the same, and the values of the cards thus exposed are used for such things as selecting who deals the game. This is often used as a pure gamble as well, much like flipping coins.