Statistical physics: For a system made up of a large number of components, a state of the system which is specified by describing the current dynamical variables of each constituting component. For example, for a gas system composed of a large number of molecules, the microstate is defined by the set of quantities which defines the state of each molecule in the system (position, velocity, vibration, etc.). In practice, it is impossible to know perfectly the microstate of a system. The aim of → statistical physics is to relate the macroscopic (average ) observables (→ pressure, → temperature, → internal energy) to the microstate of the system. Also called → microscopic state. See also → macrostate and → multiplicity.