In the game of poker, for example, the Joker can be used to complete a straight, a flush, or any other hand. Its function is to add an element of unpredictability and excitement to the game. In other games, the Joker may have different meanings and functions.

It means that the joker is a wild card. A wild card is one that can be substituted for any other card value. It is hence a very powerful card that can be used to complete all kinds of poker hands depending on which card we are missing.