Looking on the internet deeply has found these results:

An x factor is the most popular phrase on the web.

A x factor 1282,000 results on the web	An x factor 1413,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	What we look for in a car is, and I'm loathed to use the word, it's an X factor. Oscar is definitely an X factor in my theory. ! That was like an X Factor result pause! And none of them will have something, that we're really looking for on this new series of Top Gear. It's an X factor. I define it by the number of relevant facts it contains, and I define it by an X factor that I trust Will and myself to determine, using our combined five decades in the field.

A x factor

1282,000 results on the web

An x factor

1413,000 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

What we look for in a car is, and I'm loathed to use the word, it's an X factor.
Oscar is definitely an X factor in my theory.
! That was like an X Factor result pause!
And none of them will have something, that we're really looking for on this new series of Top Gear. It's an X factor.
I define it by the number of relevant facts it contains, and I define it by an X factor that I trust Will and myself to determine, using our combined five decades in the field.