FreeSync isn't the kind of technology that you see in TVs an awful lot. It does, however, appear quite frequently in computer monitors. And if you happen to have an Xbox One or Xbox One X plugged into your PC monitor, then you'll finally be able to take advantage of something rather neat.
Microsoft has announced through the Xbox Wire that all users with access to the Xbox One Preview builds will have a new option in their display and sound settings.
Titled "Allow variable refresh rate", the option basically enables support for monitors and displays that support FreeSync 2 (over HDMI). FreeSync, unveiled by AMD a few years ago, is basically improves the smoothness of gameplay by matching the refresh rate of the monitor to the frame rate, in a bid to minimise screen tearing.
The idea behind FreeSync is to eliminate tearing, but there's a huge caveat. The FreeSync tech only works across a limited range of the monitor's refresh rate, and every monitor has a different supported range. On top of that, the supported FreeSync range is much lower through HDMI - the only output supported by the Xbox One (or Xbox One X).
A list of all monitors that support FreeSync 2 over HDMI. Image: AMD
Because the bottom range of FreeSync over HDMI is usually 40Hz or 48Hz, that means FreeSync won't be much help to any game that aims for a 30 FPS lock (but drops below that). It will be helpful for 60 FPS games that dip in the low-to-mid 50s, however, so something like a Monster Hunter World on the Xbox One X would benefit a lot. (Skip to about 17 minutes below.)
It's not liable to be a feature that gets expanded upon a lot this console generation, given the lack of FreeSync support among traditional TVs, and the fact that FreeSync support is broader over DisplayPort than HDMI.
For a full list of all FreeSync supported 2 monitors, AMD has a handy table.