In the field of mathematics: X factor is an unknown number in mathematics. Unknown (unknown) is a value to be determined when solving equations, and it is also used as a metaphor for things that are not known yet. In mathematics, we often use the symbol X.

In basketball, the X factor is considered to be the person who can change the whole game situation. For example, a player's performance is not very stable at ordinary times, but occasionally a game may break out, thus affecting the whole game. Or the player himself is very powerful, and no one in the other team can stop him, but he may have injuries or other factors, and may not be able to play his ability, but once he plays his ability, it will bring victory to the team. Such a player is called the X factor.