A tesseract is a 4-dimensional object with eight cells; each cell is a cube. The tesseract is one of the six convex regular 4-polytopes. Unlike three-dimensional objects which rotate on both an axis and a plane (the plane being of length and width and the axis being of the leftover dimension, height), a tesseract rotates on two planes, one made up of length and width, and one made up of height and the fourth dimension. It is the simplest hypercube.