They are angels. The Greek word is ANGELOS, It has two meanings: the first is "messenger" and the second is "angel." In John's writings (The Gospel of John, I John, II John, III John, and the Book of Revelation) he uses the word ANGELOS 29 times; four in the Gospel of John and twenty-five times in Revelation. In all twenty-nine instances that he uses the word, it means "angel."

John also uses the word for elder - PRESBUTEROS - 14 times; once in 2 John 1:1, once in 3 John 1:1, and twelve times in Revelation. Each time he uses the word it is in reference to an elder or elders.