Those theoretical dimensions that exist beyond the sensible three (spatial) and one (temporal). Initially proposed as a relatively simple means to unify the representational equations of the four physical forces: electromagnetic force, gravitational force, strong nuclear force, and weak nuclear force. According to hyperdimensional theory, all four forces can apparently be expressed in a single equation if arrayed in ten dimensions.

Hyperdimensional theory is a subject of controversy. If you're looking for a sure shot at the Nobel Prize for Physics, all you have to do is conclusively prove that it is or isn't correct. Easy peasy.