noun

• A measure of the disorder present in a system.
• (Boltzmann definition) A measure of the disorder directly proportional to the natural logarithm of the number of microstates yielding an equivalent thermodynamic macrostate.
• (information theory) Shannon entropy
• (thermodynamics, countable) A measure of the amount of energy in a physical system that cannot be used to do work.
• The capacity factor for thermal energy that is hidden with respect to temperature.
• The dispersal of energy; how much energy is spread out in a process, or how widely spread out it becomes, at a specific temperature.
• (statistics, information theory, countable) A measure of the amount of information and noise present in a signal.
• (uncountable) The tendency of a system that is left to itself to descend into chaos.