A galleon was a large, multi-decked sailing ship
Sailing ship
The term sailing ship is now used to refer to any large wind-powered vessel. In technical terms, a ship was a sailing vessel with a specific rig of at least three masts, square rigged on all of them, making the sailing adjective redundant. In popular usage "ship" became associated with all large...

 used primarily by Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

an states from the 16th to 18th centuries. Whether used for war or commerce, they were generally armed with the demi-culverin
The demi-culverin was a medium cannon similar to but slightly larger than a saker and smaller than a regular culverin developed in the early 17th century. Barrels of demi-culverins were typically about long, had a calibre of and could weigh up to . It required of black powder to fire an round...

 type of cannon.
The term "galleon" had been in use long before the ship type that it now technically refers to came into existence. Just like the term "frigate", the term "galleon" was originally applied to certain types of war galleys in the Middle Ages.