In physics, in terms of a metric theory of gravitation, a gravitational wave is a fluctuation in the curvature of space-time which propagates as a wave, traveling outward from a moving object or system of objects.
Gravitational radiation is the energy transported by these waves.
Important examples of systems which emit gravitational waves are binary star systems, where the two stars in the binary are white dwarfs, neutron stars, or black holes.
Although gravitational radiation has not yet been directly detected, it has been indirectly shown to exist.
This was the basis for the 1993 Nobel Prize in Physics, awarded for measurements of the Hulse-Taylor binary system.