The highest display resolution of the LG 55UB820 is 4K Ultra HD. That's over four times the display resolution of a Full HD TV, which is the most frequently found 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 comparable spec TVs that have been around for around the same time as the 55UB820.
Amongst similar types of TV the worst display resolution is Full HD.
4K Ultra HD TVs have a resolution of 3840 x 2160 pixels.