[room500]

Typically, it means that if you put the TV in a dark room, it is calibrated to the same specifications that the monitors used in post-production used. Therefore, it is what the directors "intended" the video to look like since they were looking at the monitors (in a dark room).

However, if your room has even a little light in it, the settings would make the TV too dark.

It will also disable any effects the TV has that aren't "map video to screen 1:1" such as motion interpolation, upscaling algorithms, etc