For a black hole, this quantity is calculated as Boltzmann's constant times the area divided by 4 times the square of the Planck length. The Tsallis variety of it relates it to non-extensivity, and the Shannon type is used in information theory. It can be calculated for a monatomic ideal gas in the Sackur-Tetrode equation, and it is the negative derivative with respect to 
For a black hole, this quantity is calculated as Boltzmann's constant times the area divided by 4 times the square of the Planck length. The Tsallis variety of it relates it to non-extensivity, and the Shannon type is used in information theory. It can be calculated for a monatomic ideal gas in the Sackur-Tetrode equation, and it is the negative derivative with respect to temperature of Helmoltz Free Energy.  Its discontinuous nature in mixing was the subject of the Gibbs paradox, and its tendency to increase is the subject of the Second Law of Thermodynamics. For 10 points, name this quantity symbolized S, a measure of disorder.
For a black hole, this quantity is calculated as Boltzmann's constant times the area divided by 4 times the square of the Planck length.
Entropy