The thin spellbook is an inventory item that can be used to hold scrolls. It rarely drops from the orc shaman. The thin spellbook can carry 3 scrolls. It can only be used in the main inventory, but more than one thin spellbook can be used at a time. You must bring one to Magerlin for the sixth quest towards the magic skill. Alternatively you can bring Magerlin a Thick Spellbook to complete the quest. Lysis buys thin spellbooks for 142 gold and sells them for 800.