A spellbook was a type of book that wizards and other arcane spellcasters used to record their known Spells. The complex notation of a spell took up several full pages of a spellbook: the more powerful the spell, the more pages it took up. A spellbook could have any number of pages.
Copying a spell into a spellbook was a lengthy process that took up several hours and consisted of two basic steps. The first part involved mastering the fundamental elements of the spell in order to reproduce its basic form. The second part involved experimentation as the writing wizard deciphered the notation of the source, such as a Spell Scroll or another spellbook. Since each wizard typically used a unique notation, this deciphering process was always necessary. The exception was when writing a copy of one's own spellbook, in which case no experimentation was necessary since the wizard had already mastered the spell and understood their own notation.
In addition to time, the experimentation process involved in copying a spell also required the use of costly materials, such as material components spent in attempts to master the spell's basic form, as well as inscribing materials such as high-quality inks.