Not a rocket nozzle.
Whereas we mixers might have once believed that it stood for its pin outs ("ground, lead, return"), we now know that it is the catalogue code for the Cannon Connector:
"Originally manufactured as the Cannon X series, subsequent versions added a locking mechanism (Cannon XL) and then surrounded the female contacts with rubber polychloroprene insulation, which extended the part number prefix to XLR."
So there you have it, sports fans. You're all slightly smarter within a very narrow scope of knowledge. Don't say I'm not a giver.