A four-dimensional space or 4D space is the simplest possible generalization of the observation that one only needs three numbers, called "dimensions", to describe the sizes or locations of objects in the everyday world.
A four-dimensional space or 4D space is a mathematical extension of the concept of three-dimensional or 3D space. Three-dimensional space is the simplest possible generalization of the observation that one only needs three numbers, called "dimensions", to describe the sizes or locations of objects in the everyday world.