Definition of 4K in English:

4K

noun

mass noun
  • (in digital television and cinematography) technology, equipment, or content providing a very sharp image quality, with a horizontal screen resolution of around 4000 pixels.

    • ‘if 4K isn't necessary, this could be the TV for you’
    • ‘the latest games consoles are now offering gaming in 4K’
    • ‘4K TVs have become much more affordable’

Origin

Early 21st century from 4 and K, in the sense ‘one thousand’.