Samsung has it on OLED screens.

For OLED it takes very little power to dimmily illuminate a small area of the screen and the rest is the same as it’s off.

So you can do stuff like have a clock always display without having to drain your battery as much as always having the screen “on”.

But this is Apple, so who knows if they mean the standard definition or it’s like Musk’s “full self driving” that cant drive itself.