General relativity 

Einstein field equations
Equations 

Linearized Gravity
PostNewtonian formalism Einstein field equations
Friedmann equations
ADM formalism
BSSN formalism 
Solutions 

Schwarzschild
ReissnerNordström · Gödel
Kerr · KerrNewman
Kasner · TaubNUT · Milne · RobertsonWalker
ppwave 


The Einstein field equations, or EinsteinHilbert equations, or simply Einstein equations are equations that describe gravity in the classical sense. They are named after Albert Einstein and David Hilbert. The basic idea is to use geometry to model the effects of gravity. The usual form of the equations is that of nonlinear partial differential equations. Such equations are usually solved by approximation. An exact solution can be obtained in special cases, where certain assumptions are dropped, or simplified.
Mathematical Interpretation
Einstein used mathematical objects called tensors to describe the curvature of spacetime to define gravity. The equation below is the general form of the EFE :
Where R_{μv} is known as the Ricci curvature tensor, g_{μv} is the metric tensor, R is the scalar curvature, Λ is the cosmological constant, G is the gravitational constant, π is pi, c is the speed of light, and T_{μv} is called the stressenergy tensor.
Images for kids

A Swiss commemorative coin from 1979, showing the vacuum field equations with zero cosmological constant (top).