'Angel of the Lord' in the Bible

But an angel of the Lord opened the doors of the prison by night, and having brought them out said,

And when forty years were expired, there appeared to him in the wilderness of mount Sina, an angel of the Lord in a flame of fire in a bush.

And an angel of the Lord spake to Philip, saying, Arise and go southward to the way that leads down from Jerusalem to Gaza, which is desert.

And behold an angel of the Lord stood by him, and a light shone in the room; and smiting Peter on the side, he waked him, and said, Rise up quickly. And his chains fell off from his hands.

but immediately an angel of the Lord smote him, because he gave not God the glory: and being devoured by worms he died.