Dark Energy is a hypothetical form of energy that permeates all of space and is believed to be responsible for the observed acceleration in the expansion of the universe. Full definition
The energy in dark matter is equivalent to a tiny mass; there is about one pound of dark energy in a cube of empty space 250,000 miles on each side. (discovermagazine.com)
The possibilities being discussed for dark energy range from quantum vacuum energy to the influence of the unseen extra dimensions predicted by string theory. (discovermagazine.com)
But as soon as dark energy came into the picture 10 years ago, the field just exploded. (discovermagazine.com)