The X is even better in terms of performance (I think)
The Xbox One X is black, the S is white and has a little less power.
And of course the price is different.
You can find out more here:
https://www.pc-magazin.de/ratgeber/xbox-one-x-oder-s-unterschied-vergleich-kaufberatung-3200044.html
The "X" is the more powerful variant. The "S" is more or less the "Slim" (smaller size) variant of the "normal" XBox One.
So The One X has
4K gaming
12Gb RAM
6 teraflops
and more power
the one S has less power in everything
like only playing 4K movies, otherwise there's no 4K gaming