This is the average fan speed, in RPM, computed over the sampling intervals accumulated for this specific fan's live stats object. Comparing this average against the current instantaneous Speed reading on the same fan helps an admin tell whether a fan is behaving normally (hovering near its own average) or is in the middle of an unusual ramp-up or ramp-down. A fan whose SpeedAvg sits noticeably below its neighbors' averages under identical load may be spinning down prematurely due to a failing bearing.