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."
A new level of order...
"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'..."
Three years ago in a Colorado laboratory, scientists realised a long-
standing dream, bringing the quantum world closer to the one of everyday experience
In June 1995 our research group at the Joint Institute for Laboratory Astrophysics (now called JILA) in Boulder, Colo., succeeded in creating a minuscule but marvellous droplet. By cooling 2,000 rubidium atoms to a temperature less than 100 billionths of a degree above absolute zero (100 billionths of a degree kelvin), we caused the atoms to lose for a full 10 seconds their individual identities and behave as though they were a single "superatom." The atoms' physical properties, such as their motions, became identical to one another.This Bose-Einstein condensate (BEC), the first observed in a gas, can be thought of as the matter counterpart of the laser-except that in the condensate it is atoms, rather than photons, that dance in perfect unison.