for questions related to display resolutions of (virtually) 4 × HD display resolutions (each of 1,920 × 1,080 pixels), for an approx. total resolution of 4096 × 2160 pixels

Often provided on computer monitors and consumer devices as being virtually 4 HD display resolutions in a 2 × 2 array, each of 1,920 × 1,080, each giving a total single display of 3,840 × 2,160 pixels. DCI defines 4k to be 4096 × 2160.