'Angel of the Lord' in the Bible

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

But an angel of the Lord spoke to Philip, saying, "Arise, and go toward the south to the way that goes down from Jerusalem to Gaza. This is a desert."

And behold, an angel of the Lord stood by him, and a light shone in the cell. He struck Peter on the side, and woke him up, saying, "Stand up quickly." His chains fell off from his hands.

Immediately an angel of the Lord struck him, because he did not give God the glory, and he was eaten by worms and died.