En"tro*py (?), n. [Gr. &?; a turning in; &?; in + &?; a turn, fr. &?; to turn.] (Thermodynamics) A certain property of a body, expressed as a measurable quantity, such that when there is no communication of heat the quantity remains constant, but when heat enters or leaves the body the quantity increases or diminishes. If a small amount, h, of heat enters the body when its temperature is t in the thermodynamic scale the entropy of the body is increased by h &?; t. The entropy is regarded as measured from some standard temperature and pressure. Sometimes called the thermodynamic function.

The entropy of the universe tends towards a maximum.

• (thermodynamics)
  
• # strictly thermodynamic entropy. A measure of the amount of energy in a physical system which cannot be used to do mechanical work.
  
• # A measure of the disorder present in a system.
  
• # The capacity factor for thermal energy that is hidden with respect to temperature .
  
• (statistics, information theory) A measure of the amount of information and noise present in a signal.
  
• The tendency of a system that is left to itself to descend into chaos.