In the Glantri setting, each magic-user's spells are unique to him, performed in an idiosyncratic magical idiom. A magic-user's "spellbook" is actually a compilation of general-purpose magical formulae, charts and diagrams that the magic-user uses as a foundation for his spells. When a magic-user learns a new spell, he figures out how to apply this general magical knowledge in a specific way.
A magic-user may choose to transcribe his understanding of a spell into a more usable form. This transcribed spell can't be used directly by another magic-user, but it makes researching that spell significantly easier (see below). Transcribing a spell you know, or making a copy of a transcribed spell, takes one day per level of the spell.