Showdown is a term most often used in land-based casinos. It describes a situation that occurs during the river after the last round of betting in a game of poker.
After everyone has made their bets, players have to show their cards in order to determine the winner. However, some of the players reserve the privilege not to show their hands.
For example, if you end up in a two-way showdown and the other player shows their hand first and your hand is weaker, you can decide to muck. Mucking is the same as folding, and you can use it to keep your strategy secret. You won’t have to reveal how you played your hand based on the cards you were dealt or whether you have been bluffing or not.