# Dictionary

## Einstein’s equation

Einstein’s equations are the cornerstone of his general theory of relativity. They describe how the distortions of spacetime are connected with the properties (mass, energy, pressure…) of whatever matter is present.

Using a compact version of mathematical language, Einstein’s equations, a whole system of equations, can be written in an abbreviated way so that they appear to form a single equation. That’s why, sometimes, they are called “Einstein’s equation” in the singular.

An elementary description of general relativity and Einstein’s equations is given in the chapter general relativity of Elementary Einstein.