Tesseract

A tesseract (AKA 4-hypercube) is a shape equivalent to that of a 3D cube, but in “4D”. If you looked at a tesseract as a 3D being, it would look like a cube inside of a cube, connected by the vertices. Currently, we are in a 3D world, as 3D beings. We travel through 3 dimensions: X (left-right), Y (up-down), Z (forward-back). A tesseract can rotate in the W dimension, which, as a 3D being, is impossible. If you look at a cube rotating in the W dimension, it looks like 8 cubes growing and shrinking. See GIF below for further detail.