What is 4K?
4K, also known as Ultra HD, refers to a resolution of 3,840 x 2,160 pixels. That's four times the 1,920 x 1,080 pixels found in your full HD TV.
While 4K is the more commonly used term, some brands prefer to call it Ultra HD, or UHD for short. Technically, there is a difference.
Used correctly, 4K describes the 4,096 x 2160 resolution first introduced in digital cinemas. UHD refers to the 3,840 x 2,160 resolution you'll find in 16:9 ratio TVs, which is what you actually take home.
That means 4K is the wrong term for 3,840 x 2,160 displays and content, but it is used so often that the distinction has been all but lost. For most people, the two terms are interchangeable.