4D

4D usually refers to the concept of a fourth dimension beyond the familiar three spatial dimensions. In mathematics, this is formalized as four-dimensional space, often represented as R^4, with points described by four coordinates (x, y, z, w). The four-dimensional analogue of a cube is the tesseract, or hypercube, which has 16 vertices.

In physics, the phrase 4D is commonly used to describe spacetime, in which the three spatial dimensions are combined with time to form a four-dimensional manifold that is modeled by relativity. In special relativity, time is treated as a dimension with a different metric signature; in general relativity, spacetime is curved by mass-energy.

In computing and data analysis, four-dimensional data structures (4D arrays or tensors) index data by four coordinates, and are used in applications such as simulations or medical imaging.

The term 4D is also used in entertainment to describe 4D cinema or attractions that add physical effects (motion seats, scents) to three-dimensional film.

In medicine, 4D ultrasound refers to real-time 3D imaging, adding a temporal dimension to display movement.