Space is the boundless three-dimensional extent in which objects exist and events occur and have relative position and direction.

Outer space, or simply space, is the void that exists between celestial bodies, including the Earth. It is not completely empty, but consists of a hard vacuum containing a low density of particles: predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, and neutrinos. Observations have now recently proven that it also contains dark matter and dark energy.

There is no firm boundary where space begins. However the Kármán line, at an altitude of 62 miles above sea level, is conventionally used as the start of outer space for the purpose of space treaties and aerospace records keeping.