In thermodynamics and statistical mechanics contexts, the term phase space has two meanings: for one, it is used in the same sense as in classical mechanics. If a thermodynamic system consists of "N" particles, then a point in the 6"N"-dimensional phase space describes the dynamic state of every particle in that system, as each particle is associated with three-position variables and three momentum variables. In this sense, as long as the particles are distinguishable, a point in phase space is said to be a microstate of the system. (For indistinguishable particles a microstate will consist of a set of "N"! points, corresponding to all possible exchanges of the "N" particles.) "N" is typically on the order of Avogadro's number, thus describing the system at a microscopic level is often impractical. This leads to the use of phase space in a different sense.