If a normal non-filled Cube is unfolded, its six sides can be laid out (two-dimensionally) to make a cross: 4 squares going down and then 2 more on either side of the second one down. That is going from 3D to 2D.
So what is made if those six sides of the cube become cubes themselves? Folded together as 6 quares would make a Cube, these 6 Cubes would make a 4-dimensional cube/prism, called also a tesseract, however only 3 dimensions of it would be able to be seen by humans. I believe the tesseract would have 8 sides all with an even area.