Dark energy is a form of energy that acts against gravity and occupies the entirety of the universes in which it exists, uniformly across space. It acts against gravity and accelerates the expansion of them. In the observable universe, it makes up 68.3% of the total mass-energy.
Some types of dark energy with energy density that follows a certain relationship with cosmological scale have specific names. Dark energy that has constant energy density is called the cosmological constant, dark energy that follows a power-law relationship between scale and energy density is called phantom energy, and dark energy that follows an exponential relationship between scale and energy density is called black energy.