An Arcanabula, sometimes known as an orizon, is the term used for a wizard’s working spellbook; often a hodgepodge of spells (including some that were unusable by the author) and research notes for both the completed spells therein and for spell concepts still in progress.
An arcanabula differs in concept from a "travelling spellbook" in that the latter is generally a distilled copy of one or more arcanabulae, lacking the research notes for the sake of compactness, though most travelling spellbooks with blank pages remaining almost inevitably become aracanabulae.
Throughout Faerûn, the most common form of arcanabula is the spellbook that every aspiring wizard starts his or her career with. This is a well-bound book, approximately 9” x 12”, with leather-covered suthwood front and back covers protecting fifty leaves of well-crafted parchment suitable for writing on both sides (total: 100 pages), the whole weighing in at three pounds. 
The cover material varies widely from region to region, some are cloth or felt covered, some are uncovered, and some use linen paper or even vellum instead of parchment. Likewise, page counts may vary from 25 to 500 pages, though these are commonly purchased and used only after the first one has been filled to capacity.
Commonly, the front cover and/or spine bears the owner’s sigil wizard marked upon it, either visibly or invisibly. The first twenty pages or so are devoted to the research put into learning the basic cantrips, starting with spellcrafting notes which culminate in the Read Magic spell, followed inevitably by Prestidigitation and Detect Magic and progressing through the common cantrips, culminating with Arcane Mark, with which they finally gain their personal sigil “officially”. After this “cantrip section” is a grouping of spells of the first power; usually 3-7, researched in a similar manner to the earlier cantrips. After these pages, which occupy approximately one quarter of the book, the contents will depend on the owner; mostly a dozen pages or so of mixed notes and half-finished spells, with the remainder of pages still blank.
- Player's Handbook 3.5, pp. 128,131