the X Factor is called the X Factor because is used to have to buzzer which to us was the "X" so that is why it is called the X Factor
The 'X' represents the extra special "something" that the judges are looking for.
It doesn't stand for anything specific. The "X Factor" is simply the something special that a specific singer has more than the other contestants.
O2 arena in London.
Here are a couple of possibilities. There are others. (x+1) and 'x' .