- an ideal cycle of reversible engine operations in which a substance at one temperature is compressed adiabatically to a second temperature, expanded isothermally at the second temperature, expanded adiabatically from the second temperature to the first temperature, and compressed isothermally at the first temperature.
- an idealized reversible heat-engine cycle giving maximum efficiency and consisting of an isothermal expansion, an adiabatic expansion, an isothermal compression, and an adiabatic compression back to the initial state
