The Book artifact subtype was introduced in Secrets of Strixhaven, with many notable tomes, journals, grimoires, codices, journals, and other repositories of arcane knowledge getting errata’d to receive this type.
Examples of Books include white mana-heavy The Book of Exalted Deeds, its black counterpart The Book of Vile Darkness, and the pricey zero-mana Spellbook from Exodus, which gives you no maximum hand size. There is even a creature with the Book type: the fun five-color build-around Codie, Vociferous Codex.
