Spell scroll typically refers to a treasure that can be found on the adventure map. Although it is not technically an artifact, it works in a very similar way. It appears in the backpack after hero picks it up, and it can be equipped in the miscellaneous artifact slot. The scroll contains one spell, and as long as the scroll is equipped, that spell is added to the hero's spell book. However, unlike artifacts, scrolls can not be be sacrificed at an Altar of Sacrifice for experience.
It is possible to use spell scrolls and tomes to cast (Adventure map) spells even when the hero doesn't have a spell book and/or doesn't have a high enough Wisdom secondary skill to cast them normally.