Bose-Einstein condensation is a phenomenon wherein the bosons making up a substance (a boson gas) merge into the lowest energy level, into a shared quantum state. More generally it refers to the tendency of bosons to occupy the same state (closely related to stimulated emission). The state formed when a gas undergoes Bose-Einstein condensation is called a"Bose-Einstein condensate."

"The crucial distinguishing feature of Bose-Einstein condensates is that the many parts that go to make up an ordered system not only behave as a whole, they become whole; their identities merge or overlap in such a way that they lose their individuality entirely. A good analogy would be the many voices of a choir, which merge to become 'one voice' at certain levels of harmony, or the plucking of the many strings of several violins to become 'the sound of violins'..."