The difference between 4K and UHD is marginal from the customer viewpoint. Although, the Ultra HD that we have on our screen does not imply 4K from professional standards.
4K TV comes with a resolution of 4096 X 2160 pixels, the value 4096 defines its horizontal dimension, and 2160 defines the vertical, indeed. Whether a UHD TV has 3840 X 2160pixels screen resolution, almost 4-times of a Full HD TV. Since the value 3840 figures closely in 4000 so it is known as 4K UHD.
The Consumer Technology Association mentions that the standard new resolution TV is officially named UHD. Therefore, the term 4K is nothing but a synonym of UHD. It may not make such differences to see as a viewer’s eye.