In TV terms, 4K and UHD (or Ultra HD) are more or less interchangeable. 4K TVs have an increased number of pixels, resulting in higher resolution (3840 x 2160, which is a significant step up from Full HD TVs at 1920 x 1080). 8K has four times the resolution of 4K Ultra HD (7680 x 4320 pixels). Due to this, 4K and 8K TVs display incredible detail.
HDR, short for High Dynamic Range, enhances the contrast between light and dark colors. It expands a TV's ability to display a wider range of brightness, resulting in deep blacks and vibrant whites. When HDR is combined with 4K or 8K resolutions, the TV's pixels and image quality surpass that of a Full HD TV.