page_title: List of United States Marine Corps acronyms and expressions
section_title: O
hierarchical_section_title: List of United States Marine Corps acronyms and expressions / O
caption_attribution_description: English: Logo for the United States Marine Corps Officer Candidates School Source: USMC Officer Candidates School website
context_page_description: This is a list of acronyms, expressions, euphemisms, jargon, military slang, and sayings in common or formerly common use in the United States Marine Corps. Many of the words or phrases have varying levels of acceptance among different units or communities, and some also have varying levels of appropriateness. Many terms also have equivalents among other service branches that are not acceptable among Marines, but are comparable in meaning. Many acronyms and terms have come into common use from voice procedure use over communication channels, translated into the phonetic alphabet, or both. Many are or derive from nautical terms and other naval terminology. Most vehicles and aircraft have a formal acronym or an informal nickname; those are detailed in their own articles.
  The scope of this list is to include words and phrases that are unique to or predominantly used by the Marine Corps or the United States Naval Service. Recent joint operations have allowed terms from other military services to leak into the USMC lexicon, but can be found with their originating service's slang list, see the "See also" section.
context_section_description: OCONUS – Outside CONtinental United States, as opposed to CONUS.
  O-Course – Obstacle course.
  OCS – Officer Candidate School, recruit training for officers.
  O-dark thirty – Very early hours before dawn. See also military time, Zero-dark thirty. The custom of saying "oh" instead of zero has diminished, but remains in this expression.
  Office Hours – Administrative ceremony where legal, disciplinary, and other matters (such as praise, special requests, etc.) are attended, designed to dramatize praise and admonition, in a dignified, disciplined manner, out of the ordinary routine. Known as Captain's Mast afloat. An award given during a positive office hours or Mast is known as a Meritorious Mast, a negative office hours with punishment awarded is an example of non-judicial punishment.
  Officers' Country – Living spaces for officers aboard ship, or portion of post or station allocated for the exclusive use of officers.
  Oki – Okinawa.
  Old Asia Hand – Person with more than one tour in Asia.
  Old Man – Very informal nickname for the commanding officer, considered an inappropriate term of endearment for use by a junior, thus used in reference but never in address.
  OMPF – Official Military Personnel File, a record of all awards, punishments, training, and other records compiled by Headquarters Marine Corps.
  Oorah – Spirited cry used since the mid-20th century, comparable to Hooah used in the Army or Hooyah by Navy SEALs; most commonly used to respond to a verbal greeting or as an expression of enthusiasm. The origin is often disputed.
  OP – Observation Post, a position used for reconnaissance; also, the post newspaper of Marine Corps Air Ground Combat Center Twentynine Palms.
  OQR – Officer Qualification Record, a service record for officers, much like an enlisted Marine's SRB.
  OOB – Out Of Bounds, or straying into an area restricted from use by normal traffic, prohibited to Marines, or too far from base for a given liberty period.
  OOD – Officer Of the Deck, or the senior Marine responsible for the patrol and security of a unit's garrison working spaces and sleeping quarters after working hours, usually responsible for subordinate sentries and acts as a guard commander. See also duty & firewatch
  Oscar Mike – On the Move, the names of the two NATO phonetic alphabet letters O and M, which stand for the phrase. Used on the radio and in shorthand to each other. See also NATO phonetic alphabet
  OTV – Outer Tactical Vest, militarized version of Interceptor body armor, a common type of ballistic vest; being replaced by the MTV.
  Outside – Civilian life after discharge. See also real world.
  Overhead – Ceiling.
  Over the Hill – Excessively old, or a Marine so long in the service they have become institutionalized.
caption: OCS logo
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