From publisher blurb:
Compendium Arkanum introduces "multi-variable" spells to the Pathfinder Roleplaying Game.
A multi-variable spell is a spell which, once learned, you can cast as a spell one level higher or lower than the original spell. This mechanic was first introduced in Monte Cook’s Arcana Evolved. Multi-variable spells gives spellcasters great flexibility and so Tim decided to begin by adding the Heightened and Diminished qualities to Pathfinder spells.
So, in addition to the normal Pathfinder spell details, you will see one or two new bits of text, specifically, either a “Diminished Effects” line, a “Heightened Effects” line, or both. This is the first book of a set intended to include all spells from the Pathfinder Roleplaying Game Core Rulebook, Advanced Player’s Guide, Ultimate Combat, and Ultimate Magic, now with heightened and diminished effects.