Entropy means an increase of disorder or randomness in natural systems, and negative entropy means an increase of orderliness or organization. Negative entropy is also known as negentropy. Individual systems can experience negative entropy, but overall, natural processes in the universe trend toward entropy.
The concepts entropy and negative entropy are used to measure the transfer of molecules. In thermodynamics, entropy measures heat transfer. Heat flows naturally from a warmer to a cooler substance because heating molecules makes them more active, which increases their randomness. The substance that loses heat in the transfer process experiences negative entropy, but both substances as a combined system experience increased entropy.