Topology, tuh POL uh jee, is a branch of mathematics that explores certain properties of geometrical figures. The properties are those that do not change when the figures are deformed by bending, stretching, or molding. Topology makes no distinction between a sphere and a cube because these figures can be molded into one another. Topology makes a distinction between a sphere and a torus (a doughnut-shaped figure) because a sphere cannot be deformed into a torus without being torn. Topology is called rubber-sheet geometry because its figures can be deformed.