A cannon is a large, tubular gun used for projecting heavy metal balls by the force of an explosion. It was first invented in China during the 13th century and later adopted by Europeans in the 14th century. Cannons were widely used in warfare to shoot projectiles over long distances, causing significant damage to enemy troops or fortifications. The term "cannon" can also refer to a person who is considered an expert in their field, much like how one might say "he's a real cannon in the courtroom."