Oyster sauce is a thick dark brown sauce, easily confused with hoisin sauce, but made from oyster extracts (whereas hoisin sauce, which is translated as seafood sauce, is not made from any seafood). Oyster sauce is particularly popular in Cantoneses dishes, added to vegetables and noodles.
Vegetarian oyster sauce is available, made with mushrooms
Origin Story
Oyster sauce was invented or rather discovered, in 1888 by Lee Kum Sheung after he forgot about a simmering pot of oyster soup and ended up with a batch of tasty oster sludge. He formed Lee Kum Kee to market the sauce and that is now a global sauce brand.