You can always google... https://en.m.wikipedia.org/wiki/4K_resolution
a lot of meaningless comments up top 4k standard are not just square formats, ultra wide 4k is defined exactly as that LG38UC99 panel at 3840x1600. 4K name comes from the number of pixels not the screen shape, so you could have any shape you like, the wiki entry is the accepted norms of 4k outputs so people can make video content.
3840 x 1600 is what a wide 4k blue ray player will output (on a non wide screen you get black bars at the top and bottom) etc. Which is the same as the UC99 panel. LG calls it QHD+ - it is still 4 x the resolution of an 1080 screen.
