When people talk about Ultra, they are usually talking about game settings, not resolutions. However, UltraHD is 4K if I'm not mistaken.
1600p and 1440p don't have an HD definition that I'm aware of. These HD definitions are for TV's, and those two resolutions are not TV related. PC users just say their resolution, and leave the HD stuff to TV's.
When people talk about Ultra, they are usually talking about game settings, not resolutions. However, UltraHD is 4K if I'm not mistaken.
1600p and 1440p don't have an HD definition that I'm aware of. These HD definitions are for TV's, and those two resolutions are not TV related. PC users just say their resolution, and leave the HD stuff to TV's.