Mathematical concept of the fourth spatial dimension (this is not about time as the fourth dimension, aka spacetime).
#1: (1:10) Obviously your room would only exist in a single 3d space. Technically, the room described here is actually 4-dimensional.
#2: (2:30) This is a 2d object (ie, unlike a piece of paper), which means there is no no “front” or “back” – so you can see all the points at once.
#3: (4:31) For this analogy, we are comparing the act of drawing on an ordinary canvas, on both the 3d and 4d worlds. Carving, sculpting and creating 3d models on the computer don’t change the fact that humans can not “draw” a real 3d shape by hand on a “flat” surface.
#4: (5:49) The 3d objects and the light source are on different 3d spaces.