In thermodynamics, an isothermal process is a type of thermodynamic process in which the temperature T of a system remains constant: ?T = 0. This typically occurs when a system is in contact with an outside thermal reservoir, and a change in the system occurs slowly enough to allow the system to be continuously adjusted to the temperature of the reservoir through heat exchange (see quasi-equilibrium). In contrast, an adiabatic process is where a system exchanges no heat with its surroundings (Q = 0). https://en.wikipedia.org/wiki/Isothermal_process