Performance Bonus
A performance bonus is a special bonus type that can generally only be applied by bards. Like arcane or divine bonuses, Performance Bonuses do not stack with other Performance Bonuses, even if the two bonuses are attempting to boost totally different character attributes. If a new song, spell, or effect attempts to apply a new Performance Bonus on a character or creature that already has an existing Performance Bonus, the subject must immediately choose to either keep their existing Performance Bonus, or replace it with the new Performance Bonus.
A Performance Bonus can be stacked with an Arcane Bonus or a Divine Bonus (as well as any other bonus type, other than another Performance Bonus), unless the effect being placed upon the target is coming from an effect with the same name as the Performance Bonus. This means you can benefit from a buffing effect created by a bard, and a different buff spell cast by a divine caster at the same time, even if both effects improve the same attribute (such as armor class), unless both effects share the same name. (Note that 'same name' excludes the parenthetical in the page title, meaning that Stoneskin (Druid Spell) and Stoneskin (Sorcerer/Wizard Spell) are considered the same spell for this purpose.)
Most performance bonuses come from bardic performances (i.e. songs), and no creature may ever be the target of more than one song at the same time, even if more than one bard is performing.