The rate at which the temperature of a parcel of dry air decreases as the parcel is lifted in the atmosphere. The dry adiabatic lapse rate (abbreviated DALR) is 5.5°F per 1000 ft or 9.8°C per km.
The rate of decrease of temperature with height when unsaturated air is lifted adiabatically (without exchange of heat with its surroundings). The decrease is due to expansion as the air is lifted to a lower pressure.
The rate of cooling (by expansion) as an air parcel rises, if no other additions of heat occur. It is approximately 10 degrees Celsius per kilometer, or 5 degrees Fahrenheit per thousand feet. It is also the rate of heating (by compression) as an air parcel descends.