'Angel of the Lord' in the Bible

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

And forty years being fulfilled to him, the Angel of the Lord appeared to him in the desert of Mount Sinai in a flame of fire in a bush.

And the angel of the Lord spoke to Philip, saying, Arise and go toward the south, on the way that goes down from Jerusalem to Gaza, which is a deserted place.

And behold! An angel of the Lord stood by, and a light shone in the building. And striking Peter's side, he raised him up, saying, Rise up quickly! And his chains fell off his hands.

And immediately the angel of the Lord struck him, because he did not give God the glory. And he was eaten by worms and gave up the spirit.