THE X-FACTOR

what exactly does one mean when he says a person's got the x-factor?

is it a term strictly pertaining to looks, personality, feel?

when people are asked how they feel about the x, they simply shrug and say "i don't know what it is, but she's got it."

hmm.

so i can only deduce that the letter "x" is used in "x-factor" as it would be in an algebraic equation.

it is to be replaced by some word or something.

and it need not be positive.