guys in torishop there are some things that cost 10.00 tc... these things are called set.... but what do?

You've mean this?
The Set boxes are using for item storaging and organizing your inventory instead of making a huge mess in your inventory.

It's not an item for in-game, as FighterKHV said: It's just some kind of box you can put items in. Then you rename it.
For example: I have 5 orc forces, 3 orc relaxes and some orc gradients.
I don't want that mess all over my inventory, so I buy a new set, call it "Orc" and put all of the orc items inside.

You can sell sets, which means the user gets a box and the items inside.