Stuff is all sorts of things - Armor, weapons, items - created by Stuffamancy.
According to LIAB_Text_40, stuff may be polarized by a particular discipline (Thinkamancy is mentioned), and may be imprinted by Signamancy. The Vibrations of Grandiocosmic Strings cannot penetrate polarized stuff according to Isaac. LIAB Text 40
Stuff has several characteristics:
- Color and shape (Signamancy)
Essentially what we call "Matter".
Some say all Stuff is Magic, that the two are the same thing.