Where does the phrase “alpha and omega” come from and What does alpha and omega mean?

The expression “alpha and omega” means: The first and the last; the beginning and the end.

Both the expression itself, the first and the last letters of the Greek alphabet, and its definition are from the Bible, The Revelation of St. John the Divine.

The phrase is repeated four times, in the eighth and eleventh verses of the first chapter, in the sixth verse of the twenty-first chapter, and in the thirteenth verse of the twenty-second chapter.