Oscar Mike to the glossary. Copy that.
Historically, Britain's middle-class farmer-soldiers who owned their own land and occasionally cosplayed as cavalry when the homeland needed defending. Starting in 1761, these landed gentry types formed volunteer mounted units that eventually merged into the Territorial Army. Think of them as the original weekend warriors, except with actual horses and significantly better real estate holdings.
A guttural battle cry and motivational exclamation unique to the Marine Corps, expressing enthusiasm, aggression, or acknowledgment. The more 'yut,' the more motivated the Marine.