4K is roughly 3840 by 2160 pixels, four times the pixel count of 1080p. On a screen network it is now the default on new commercial panels rather than a premium option.
Where it genuinely helps is close viewing. A wayfinding kiosk, a spec sheet at arm's length, or a menu with small print all benefit from the extra density, because the viewer is near enough to resolve it.
The caveat is that at normal signage viewing distances, most people cannot tell. A screen read from four metres shows no visible difference between 1080p and 4K content, so the resolution buys nothing on the wall, while costing across the whole pipeline: four times the file size to distribute, more decoding capacity in the player, and storage that grows accordingly.
The practical trap is a 4K panel fed by a player that cannot decode 4K smoothly, producing stutter that looks worse than clean 1080p. Match the player to the panel, and author to the distance the content is actually read from.