Twist rate is the number of rotations, almost always ( 1 ), in a given number of inches. In this case, 1 in 9 means the bullet will complete one full rotation within the barrel for every 9 inches of barrel travelled. If you have an 18 inch barrel, the bullet will make 2 full rotations before leaving the bore.
As to twist rate being good or bad, that is almost wholly in relation to the grain bullet you are using. I am no expert, of that I can assure you, so you need to ask the reloading guys, but generally, certain twist rates are better suited for a certain range of bullets.
has a good discussion of twist rates that I think will help considering your intended purchase.