The 40PUH6400 has a maximum display resolution of 4K Ultra HD. That's over four times the display resolution of a Full HD television, which is the most common display resolution. 4K Ultra HD TVs have a resolution of 3840 x 2160 pixels.
A 4K Ultra HD HD type is in fact the best display resolution amongst all TVs of a comparable spec and age to the 40PUH6400.
Amongst comparable types of TV the worst display resolution is HD Ready.
4K Ultra HD TVs have a resolution of 3840 x 2160 pixels.
There are a number of alternative 4K Ultra HD TVs currently available which you might want to consider including cheaper TVs such as the Samsung UE48JU6445, or the LG 40UF671 (£605.36).