Universe/ˈjuːnɪvɜːrs/ Definition 1 of 5Pro Tip 1/3All-Inclusive Refers to everything that exists, with no exceptions. The universe encompasses all matter and energy. Pro Tip 2/3Not Interchangeable 'Universe' and 'galaxy' are not the same; a galaxy is part of the universe. The Milky Way is just one of billions of galaxies in the universe. Pro Tip 3/3Scientific Context Often used in discussions about physics, astronomy, and cosmology. The universe is expanding at an accelerating rate.