If we knew how to create world simulation, and how to make it working 4D, then humans would be able to plug themselves in, and experience 4D space. Alternatively there could simulated 4D beings, whose sentience could be transferred to robot body in our real 3D space.
Another space dimension, which has same relation to our three X Y Z dimensions, as third dimension Z relation to X Y.
For clarity the word is perpendicularity. A 4th spatial dimension would have to be perpendicular to all 3 other spatial dimensions.
Ah I understand you now, I was confused about you not specifying space when referring to 4D, mb.