The term "power balla" is a colloquialism used to describe a type of song performed (but not necessarily written) by a hard rock or heavy metal band that is atypical of the songs defined by the hard rock and heavy metal genres. Typically, a power ballad is characterized by having a slower tempo, longer voiced notes, acoustic guitars in place of electric guitars, and deemphasized percussion and bass; but some sections of the song may include strong percussion and bass that are more typical of the hard rock and heavy metal genres for increased emotional effect. Common power ballad themes include (but are not limited to) emotional heartache, need, love and loss.