It is common and often heard that people say "G.I." in the United States. In literal, they use "G.I." in conversations. What is "G.I."?
People say GI referring to the member of US soldier or their equipment. Many thought it was an acronym of "Government Issue"; however, the original term is galvanized iron(鍍鋅，俗稱馬口鐵) and GI was used to denote the military equipments, such as metal trash can, which was made from it in US Army inventories or supply records. During World War I, it was somehow assumed that GI stood for "General Issue". The term even farther referred to all military equipments and soldiers themselves afterwards.
Extensively, G.I. generation is the cohort of Americans who fought in World War II. G.I. Joe was the famous military-figure toy during 60s, who first came out from a comic strip on US military magazines during WWII.