The story
From the name of fine XO (extra-old) cognac, which (though not an ingredient of the sauce) denotes high quality, prestige, and luxury in Hong Kong.
Etymology from Wiktionary, CC BY-SA 4.0.
XO sauce
Today it means: A spicy sauce from Hong Kong, made from roughly chopped dried seafood, chili peppers, onions, and garlic. Full definition →