A factor that expresses the dynamic efficiency of the bow and arrow combination. It is the weight in grains of an imaginary mass shot from the bow bow at the indentical instant and with the identical velocity as the arrow.
HA!
So I WAS right!
Wasn't I?
I guess they needed all that gobbly gook to justify all the money they spent on their education, when "It tells you how efficient your bow passes it's stored energy to an arrow, and the more efficient your bow is, the more energy it will pass".