Source: Player's Handbook
You can cast spells to greater effect.
Benefit: All variable, numeric effects of an empowered spell are increased by one-half. An empowered spell deals half again as much damage as normal, cures half again as many hit points, affects half again as many targets, etc., as appropriate. For example, an empowered magic missile deals one and one-half times normal damage (roll 1d4+1 and multiply the result by 1.5 for each missile). Saving throws and opposed rolls (such as the one you make when you cast dispel magic) are not affected. Spells without random variables are not affected. An empowered spell uses up a spell slot two levels higher than the spell's actual level.