1. The rate of decrease with height for an atmospheric variable.

The variable involved is temperature unless specified otherwise. The lapse rate is the rate of decrease with height and not simply the rate of change.

While most often applied to the earth's atmosphere, the concept can be extended to any gravitationally supported ball of gas.

2. The rate of decrease of temperature with elevation in the atmosphere.

The environmental lapse rate is determined by the distribution of temperature in the vertical at a given time and place and should be carefully distinguished from the process lapse rate, which applies to an individual air parcel.