Plain English Meaning
The fastest you are allowed to descend on final approach so you stay on the correct glide path. The faster you are flying over the ground, the steeper the descent in feet per minute needs to be to stay on profile -- but the chart gives you a ceiling you should not exceed.
Full Definition
The highest rate of descent, in feet per minute, that a pilot may use on the final approach segment of an instrument approach without going below the published vertical path or descent profile. These rates are tied to the aircraft's groundspeed and the descent angle of the approach, and they are tabulated on so can confirm a safe rate of descent for the being flown.