Pronominal verbs are a category of verbs that use the reflexive pronoun (“se”). It includes reflexive verbs, reciprocal verbs, and idioms.
The part that bit me today was that all pronominal verbs use être instead of avoir as their auxiliary verb.
Il a promené le chien. He had taken his dog for a walk.
Il s’est promené. He had gone for a a walk.
Il a lavé le chien. He had washed the dog.
Il s’est lavé les mains. He had washed his hands.
(When referring to parts of the body, it’s normal to use the reflexive pronoun and the definite article.)
Ah, the joys of brushing up on grammar.
About.com has a decent write-up on French pronominal verbs.