The 55PUS7909 has a maximum display resolution of 4K Ultra HD. That's over four times the display resolution of the most common HD type of Full HD. 4K Ultra HD TVs have a resolution of 3840 x 2160 pixels.
This TV's display resolution (4K Ultra HD) is actually the best display resolution amongst all large TVs that were released around the same time as the 55PUS7909.
The worst display resolution amongst similar types of TV is Full HD.
4K Ultra HD TVs have a resolution of 3840 x 2160 pixels.
Other 4K Ultra HD televisions currently available that you might also want to look at include because of it's better review score, the Sony FWD-55X8600.