S-Rank Weapons?

[Arross]

Can someone please explain what exactly S-rank weapons are, how you get them, and what you can do with them?

[Ketchup345]

http://www.pso-world.com/viewtopic.php?topic=84006&forum=17&14

Let me add that the reason they are strong is because of their high grind value. They also have consistant damage.