What is 4K Blu-ray?

Ultra HD 4K Blu-rays have the best picture quality possible for your 4K TV. Look out for discs that have high dynamic range (HDR) and wide color gamut (WCG) which will produced a much more noticeable improvement.

Other technical improvement over regular Blu-ray includes:

  1. 10 bit colour – so more steps of graduation
  2. Higher frame rates
  3. H.265 – latest codec
  4. Greater capacity disc – 4K Blu-rays will have 66GB or 100GB capacity
  5. Audio – new audio formats such as Dolby Atmos and DTS:X

Source: What is 4K Blu-ray? – CNET