Macroscopic systems in a thermal equilibrium state may, despite their very large number of degrees of freedom, be characterized by only a small set of quantities such as pressure, volume, particle number and temperature. In physics, one refers to this kind of description as a thermodynamical description. This description works very well for equilibrium states because, with increasing number of particles, an overwhelming majority of the system's microstates have the same macroscopic properties. Microstate here refers to a description that includes all degrees of freedom of the system under study. As a result of the above tendency, thermodynamical behaviour becomes ‘typical’. In more technical terms this fact is called the existence of the thermodynamic limit, meaning that intensive quantities, such as the energy per particle, approach a limiting value that does no longer depend on the detailed configuration of the system as its size increases. As an example, the energy per particle of a very large piece of solid is independent of whether this piece is surrounded by air or water, provided it is in an equilibrium state, i.e., has the same temperature as its surrounding.