What are angels? Basically, they are considered as beings, transcendental ones, who do the bidding of a supreme divine being. Angels can be found in different literature throughout our history. Different religions have different names for them but most agree on their function as servants of a divine being.
There have also been debates about whether angels have free will. They are usually described as beings who usually come to earth as commanded by God to bring a message or sometimes act as the hand for divine intervention.
The bottomline is, angels are what you believe they are. Literature may have its own stand about angels, but it does not mean you can't also have yours. Just believe in what you think they are - whether they be teeny angels or a glorious being emanating a blinding glow.
