Dark energy is is a catch-all term for any form of energy that is not visible to observers on Earth. For example, measurements have shown that the known universe is not only expanding, the rate of expansion is increasing. Scientists have not been able to determine where the energy for this acceleration is coming from, so they have labeled it "dark energy".
Dark matter is a related term.
Dark Energy in Science Fiction
- The Tesseract in the Marvel Comics cinematic universe is a powerful source of dark energy.