the Dark Continent a name given to Africa by Europeans in the 19th century. The name meant that Africa was then an unknown area to Europeans, but it is now considered an offensive name.
cosmology the unknown energy thought to make up about 70 per cent of the observed total in the universe, associated with a negative pressure that makes the universe expand faster; the simplest form of dark energy is a cosmological constant, however more general models allow for an evolving energy density and pressure