In the United States, it means the lowest three enlisted rates of the U.S. Navy and U.S. Coast Guard, followed by the higher petty officer ranks. The equivalent of the seaman is the matelot in French-speaking countries, and Matrose in German-speaking countries.
The term "seaman" is also a general-purpose for a man or a woman who works anywhere on board a modern ship, including in the engine spaces, which is the very opposite of sailing. This is untrue in the US Navy where a sailor might be a seaman but not all US Navy sailors are a 'Seaman' as they might be an Airman, Fireman, Constructionman, or Hospital Corpsman. Furthermore, "seaman" is a short form for the status of an "able-bodied seaman," either in the navies or in the merchant marines. An able-bodied seaman is one who is fully trained and qualified to work on the decks and superstructure of modern ships, even during foul weather, whereas less-qualified sailors are restricted to remaining within the ship during times of foul weather — lest they be swept overboard by the stormy seas or by the high winds.
The Royal Australian Navy features one Seaman rank.
There are 4 grades of seaman/matelot in the Royal Canadian Navy:
Ordinary seaman or matelot de troisième classe