In thermodynamics entropy is the heat transferred into a system divided by the temperature, or if Q is the heat transferred, then we say ΔS = Q/T. The "Delta" means change in. Entropy was a focus of the work of Ludwig Boltzmann and his grave site has the formula he found describing its statistical character. Although it was discovered by studying heat transfer, we now understand that entropy is a measure of what characteristic of a system? Hint: the universe is changing to increase its entropy.