4D

4D, meaning the common 4 dimensions, is a concept in mathematics. It has been studied by mathematicians and philosophers since the 18th century. Mathematicians who studied four-dimension space in the 19th century include Möbius, Schläfi, Bernhard Riemann, and Charles Howard Hinton.
In geometry, the fourth dimension is related to the other three dimensions of length, width, and depth by imagining another direction through space. Just as the dimension of depth can be added to a square to create a cube, a fourth dimension can be added to a cube to create a tesseract.
4D is also an important idea in physics, developed in the 20th century. In physics, it refers to the idea of time as a fourth dimension, added to the (3D) spatial dimensions. Albert Einstein developed the idea of spacetime by connecting space and time together. The difference is that spacetime is not a Euclidean space, but instead is called "Minkowski spacetime".