Describing 4K is easy, justifying it is another story
The Pledge: what is 4K?
For most people, 4K or "Ultra HD" is a "really high resolution" that, for most purposes, uses approximately four times the pixels of a typical HD (in this case, 1080p) image. This pretty much applies to the really expensive televisions seen in electronic retailers, and is touted as the next best thing for video. Just as with photographs, higher resolutions are better for seeing more detail in footage, potentially allowing viewers to see more than they would have via normal HD video. I won't blame you if you decide to skip down to the next subheading, if you want to just move on to the justification element.
Ignoring the various "standard definition" resolutions used around the world for normal television broadcasts, 1080p is classed as an image with a resolution of 1920x1080 pixels. Technically, 4K is covered by two different definitions, with the DCI 4K standard referring to a 4096x2160-resolution image, with a 1.9:1 aspect ratio, though this could be ignored for our purposes, as it's typically used in film and video production only.