Closed system

A system which is considered to be isolated, totally or practically, from its environment such that there is no significant import or export of energy in any of its forms such as information, light, heat, physical materials, etc. and therefore no change of the components of the system. An open system becomes closed if input and output is cut off. Some open systems become effectively closed if either input or output is terminated, thus cessation of throughput is also a factor since it may also terminate input or output or both. In thermodynamic terms if, in an open system, momentum or conversion of energy ceases, the system may close.