Vancian

Refeering to the author Jack Vance, a perpetrator of the 'dying earth' genre of fantasy fiction. In roleplaying games the term 'vancian' became notable because the Dungeons & Dragons magic system, specificaly the way Wizards use spellbooks and memorize a certain number of spells per day was based on the magic system Vance used in his books.

4E has mostly dropped this magic system and went for a more Harry Potter feel but it obviously remains in its most pure form in the Jack Vance's Dying Earth RPG.