Fire return interval describes the average period of time between fires experienced by a given area. This is also referred to as the mean fire return interval. When using fire return interval, the size of the area must be specified.
Source: Hardy, Colin C., Ottmar, Roger D., Peterson, Janice L., Core, John E., and Seamon, Paula. 2001. Smoke Management Guide for Prescribed and Wildland Fire 2001 Edition. Produced by the National Wildfire coordinating Group Fire Use Working Team.