The rather wonderful word 'angelology' means "The Study of Angels". It comes from the Greek word 'angelologia', which is a combination of two words: ANGELOS (angel, original meaning: messenger) and LOGOS: word.
Recently I stumbled across a Dictionary of Angels (including the fallen angels) and I have really enjoyed reading it. Or maybe I should say: dipping into it, as it contains enough information to make your head spin.
The concept angel is often associated with the Bible and the Christian belief system. This is a misconception as many angels appear in other sources too.
All cultures acknowledge the existence of spirits at levels beyond the human. We call them angels, but in other traditions they go by different names.