What does the idiom head and shoulders above the rest mean?

If someone is literally head and shoulders taller than another person in height, it would be obvious. There would be no dispute as to who is taller. Taken figuratively, it would mean that another person or thing is indisputably much better than the rest.

I believe that the phrase refers back to a description of Saul who was described in 1 Samuel 9:1-2 as "a handsome young man. There was not a man among the people of Israel more handsome than he; from his shoulders upward he was taller than any of the people."