Morue is salt cod (cabillaud), although in some parts of France morue is also used for the fresh fish, especially young cod (morue fraîche).
Nearly every fish stand has slabs of salt cod waiting to be purchased and soaked for several days to soften and remove the salt. You can also buy it vacuum packed and pre-soaked, but even then it’s a bit salty and needs to be soaked at least over night. It’s very popular among the large Portuguese community in France.
Brandade is probably the most famous French salt cod dish, along with accras. Up north you may see joues et langues de morues dunkerquoises (Dunkirk-style cod cheeks and tongues)—sautéed with onion and garlic and parsley.
Morue is also a not very nice slang word for a loose woman or a prostitute.
Image by cucina buttalapasta