The microcanonical ensemble from physics provides an informal example. Consider, for example, a fluid, gas or plasma in a box of width, length and height formula_39 consisting of formula_40 atoms. A single atom in that box might be anywhere, having arbitrary velocity; it would be represented by a single point in formula_41 A given collection of formula_40 atoms would then be a "single point" somewhere in the space formula_43 The "ensemble" is the collection of all such points, that is, the collection of all such possible boxes (of which there are an uncountably-infinite number). This ensemble of all-possible-boxes is the space formula_2 above.