What is 4K (UHD)?
A UHD image contains over 8 million pixels, while a Full HD image only contains 2 million pixels. As a result, the UHD resolution is 4 times as sharp. You can especially see the difference in sharpness on screens starting at 40 inches. In order to watch UHD images, both the TV and the source must support this resolution. This can be a UHD Blu-ray player or a console, but video service such as YouTube and are also starting to offer UHD videos.
The 4K resolution is an industry standard for movie theaters and is made up of 4,096x2,160 pixels. The difference with UHD is that the row of horizontal pixels is wider because movie theater screens are wider than television screens. Still, 4K is closely intertwined with the TV industry's UHD. During your search for a TV, you can assume that both 4K and UHD refer to the same thing.