This is the highest fan speed, in RPM, that UCS Manager has recorded for this specific fan across the sampling intervals covered by its live stats object. A SpeedMax that regularly approaches the fan's mechanical ceiling suggests the server has been running hot enough to require maximum cooling, which is worth cross-checking against the chassis's ambient and CPU temperature readings. This value resets when the interval window rolls over, so a persistently high max over successive windows points to sustained thermal pressure rather than a single brief spike.