4K is an newer ultra high resolution video format. The “4K” refers to the 4096 pixels across that make up the frame.
There are two types of 4K video format. The ‘professional’ format is 4096 x 2160 (17:9) and referred to as 4K DCI. The more common format is 4K UHD with a format of 3840 x 2160 (16:9).