Not giving out or receiving heat.

Of or denoting change in volume or pressure, with no heat gain or loss with the surrounding air.

(adj.) A process where no heat enters or leaves the system. In the atmospherie, when air rises, it expands because of a reduction in pressure. In the absence of non-adiabatic processes (condensation, evaporation, radiation), expansion causes the air to cool at about 1 degree per 300 feet.

A process in which there is no heat transfer, thus its temperature-entropy graph is a vertical straight line, and thus entropy is constant during the process.