What do the number in 9X7 hub motor mean

[hekdude]

I have been searching through the board, and am still confused what the 9 and the 7 mean in a 9X7 hub motor. I gather that the 7 is the turn count, but what is the 9?

 

[Ykick]

http://endless-sphere.com/forums/viewtopic.php?f=2&t=21957

 

[hekdude]

thanks