Reference

Military Glossary

Plain-English definitions for U.S. military terms, acronyms, and jargon used across all six branches.

A B C D E F G J L M N O P R S T U W X

A

Active Duty: Full-time military service, as opposed to Reserve or National Guard part-time service. Active-duty service members serve 24/7 and are subject to deployment at any time.; See also: Reserve, National Guard
AFSC: Air Force Specialty Code. A five-character alphanumeric code identifying an Air Force member's job specialty (e.g., 1A8X1 is Airborne Cryptologic Linguist).
ASVAB: Armed Services Vocational Aptitude Battery. A standardized test taken by all military enlistment candidates. Scores determine eligibility and job placement across every branch.
AWOL: Absent Without Leave. When a service member leaves their post or duty station without authorization. A criminal offense under the UCMJ that can result in discharge or court-martial.

B

Battle Dress Uniform (BDU): The camouflage combat uniform used by the U.S. military before the introduction of branch-specific combat uniforms in the 2000s. Colloquially still used to refer to any military camouflage pattern.; See also: ACU, OCU
Billet: A specific assignment or position within a unit or command. Also used informally to mean sleeping quarters aboard a ship or at a military installation.
Boot Camp: The initial entry training program for enlisted recruits, designed to transform civilians into military service members through physical conditioning, discipline, drill, and basic soldiering skills. Officially called Basic Combat Training (Army), Recruit Training (Navy/Marine Corps), Basic Military Training (Air Force/Space Force), or Basic Training (Coast Guard).
Brigade: A military unit larger than a regiment and smaller than a division, typically composed of two to five battalions. In the Army, brigades contain roughly 1,500–3,200 soldiers and are often organized as Brigade Combat Teams (BCTs).

C

Chain of Command: The line of authority and responsibility through which orders are passed from the most senior commander down to individual service members. Maintaining the chain of command is a core military principle.
CIB: Combat Infantryman Badge. An Army decoration awarded to infantry and Special Forces officers and enlisted soldiers for being under enemy fire in active ground combat.
CO: Commanding Officer. The officer in command of a military unit, ship, installation, or aircraft. Also abbreviated as 'the CO.'
CONUS: Continental United States. Refers to the 48 contiguous states and the District of Columbia. 'OCONUS' refers to all other locations, including Alaska, Hawaii, and overseas assignments.
Corpsman: A Navy enlisted medical specialist (Hospital Corpsman, rating HM) who provides medical care to Navy personnel and frequently serves embedded with Marine Corps units as the primary medic.
Court-Martial: A military court convened to try service members accused of violations of the Uniform Code of Military Justice (UCMJ). There are three levels: summary, special, and general court-martial, with increasing severity.

D

Deployable: A service member or unit that is medically, legally, and administratively cleared to be sent to a forward or overseas assignment on short notice.
Deployment: The movement of military personnel or assets to an area of operation. Deployments can be for combat, training, peacekeeping, humanitarian assistance, or deterrence missions.
DFAC: Dining Facility. The military's term for a cafeteria or mess hall on a military installation or forward operating base. Pronounced 'dee-fac.'
Discharge: Formal separation from military service. Types include Honorable Discharge, General Discharge (Under Honorable Conditions), Other Than Honorable (OTH), Bad Conduct Discharge (BCD), and Dishonorable Discharge — each carrying different benefits and legal implications.
Division: A major tactical unit, typically composed of 10,000–20,000 soldiers across multiple brigades. Army divisions are the primary fighting formation for large-scale combat operations and are commanded by a Major General.
DoD: Department of Defense. The federal executive department responsible for coordinating and supervising all agencies and functions of the government concerned directly with national security and the United States Armed Forces. Headquartered at the Pentagon.

E

E-1 through E-9: The enlisted pay grade scale, running from the most junior (E-1: Private in the Army) to the most senior (E-9: Sergeant Major of the Army / Master Chief Petty Officer of the Navy, etc.). Grade titles differ by branch.
Enlisted: Service members who enter the military through enlistment rather than commissioning. Enlisted personnel make up approximately 83% of the force. They are led by noncommissioned officers (NCOs) at the senior enlisted levels.

F

Field Grade Officer: Officers in the grades of O-4 (Major), O-5 (Lieutenant Colonel), and O-6 (Colonel). Distinguished from Company Grade officers (O-1 through O-3) and General/Flag officers (O-7 and above).
FMSS / FOB: Forward Operating Base (FOB). A secure, semi-permanent position in a forward combat area, used to support tactical operations and reduce response time.
Flag Officer: A general or admiral — any officer of O-7 rank or above (one to four stars). Called 'flag officers' because they are entitled to fly a personal flag denoting their rank and command.

G

GI: Government Issue — a colloquial term for a U.S. military enlisted service member, especially a soldier. Originated in World War II and remains in common use.
General Order: A formal, numbered directive issued by a senior commander that applies to all personnel under that command. Also refers to the standard standing orders all military sentries are required to memorize.

J

JROTC: Junior Reserve Officers' Training Corps. A citizenship and leadership program offered in high schools, sponsored by each of the four military departments. JROTC graduates may receive advanced enlisted rank upon enlistment but are not required to join the military.
Joint: Involving two or more branches of the U.S. Armed Forces. Joint operations, commands, and exercises are a central feature of modern U.S. military doctrine (e.g., Joint Chiefs of Staff, Joint Task Force).

L

Leave: Authorized paid vacation time for military service members. Active-duty members accrue 30 days of leave per year. Unlike civilian vacation, leave must be formally approved and can be canceled during emergencies.

M

MOS: Military Occupational Specialty. The Army and Marine Corps code identifying an enlisted service member's job (e.g., 11B is Army Infantryman). The Air Force uses AFSC; the Navy uses 'rating'; the Space Force uses SFSC.
MP: Military Police. Soldiers in the Army Military Police Corps (31B MOS) who enforce laws and order on military installations, conduct combat support operations, and assist civilian law enforcement in some circumstances.
MRE: Meal, Ready-to-Eat. Self-contained individual field rations issued to service members in the field when hot food service is unavailable. Each MRE provides approximately 1,250 calories and a 3–5 year shelf life.

N

NCO: Noncommissioned Officer. Senior enlisted service members (typically E-4 or E-5 and above, depending on branch) who hold leadership authority over junior enlisted troops. NCOs are the backbone of the military — they train, discipline, mentor, and care for the soldiers, sailors, and Marines under their charge.; See also: Enlisted, Officer
NJP: Non-Judicial Punishment. Disciplinary action taken by a commanding officer under Article 15 of the UCMJ, without a court-martial. Also called 'Article 15' (Army/Air Force), 'Captain's Mast' (Navy/Marine Corps), or 'Admiral's Mast.'

O

O-1 through O-10: The commissioned officer pay grade scale, from Ensign/Second Lieutenant (O-1) to Admiral/General (O-10). Officers are commissioned via service academies, ROTC, or Officer Candidate School.
OCONUS: Outside the Continental United States. Any assignment in Alaska, Hawaii, U.S. territories, or foreign countries.
OCS / OTS: Officer Candidate School (Army, Navy, Coast Guard) / Officer Training School (Air Force, Space Force). Programs that commission civilians and enlisted members as officers, typically in 10–13 weeks.

P

PCS: Permanent Change of Station. A military assignment that moves a service member and their dependents from one duty station to another. Most service members receive a PCS every 2–3 years.
Pentagon: The headquarters of the U.S. Department of Defense, located in Arlington, Virginia. The five-sided building, completed in 1943, is the largest office building in the world by floor space and houses approximately 23,000 military and civilian employees.
PT: Physical Training. Organized physical fitness exercises conducted by military units, typically in the early morning. PT standards are defined by each branch and must be met to pass periodic fitness assessments.

R

Rank: The formal grade of authority and precedence held by a service member, displayed through insignia on the uniform. Rank determines pay, authority, responsibility, and protocol. See the Ranks section of this site for complete tables by branch.; See also: NCO, Enlisted, Officer
ROTC: Reserve Officers' Training Corps. A college-based officer commissioning program offered at hundreds of universities. Army ROTC, Naval ROTC (commissioning Navy and Marine Corps officers), and Air Force ROTC (commissioning Air Force and Space Force officers) are the three programs.

S

SIGINT: Signals Intelligence. The collection and analysis of electronic signals — including communications, radar, and weapons systems — to produce intelligence. A critical intelligence discipline managed by the NSA and service intelligence elements.
SOP: Standard Operating Procedure. A documented, step-by-step process for conducting a recurring task or mission. SOPs reduce errors, ensure consistency, and allow units to operate without constant supervision.

T

TDY / TAD: Temporary Duty (TDY, used by Army/Air Force/Space Force) or Temporary Additional Duty (TAD, used by Navy/Marine Corps). Short-term assignments away from a service member's permanent duty station.
Theater: A defined geographic area in which military operations are conducted. Examples include the Indo-Pacific Theater (INDOPACOM) and the European Theater (EUCOM).
Top Secret / SCI: Classification levels for national security information. Top Secret is the second-highest civilian classification. Sensitive Compartmented Information (SCI) is a subset of Top Secret requiring additional access controls and compartmented 'read-ins.'

U

UCMJ: Uniform Code of Military Justice. The federal law that defines criminal offenses and judicial procedures for all U.S. military personnel. Enacted in 1950, it covers 146 punitive articles ranging from absence without leave to espionage and murder.

W

Warrant Officer: A specialized technical expert or aviator who holds a rank between senior enlisted and commissioned officer. Warrant officers (W-1 through W-5) are used by the Army, Navy, Marine Corps, and Coast Guard for highly specialized roles such as helicopter pilot, CID investigator, or IT systems technician.; See also: Enlisted, Officer, NCO

X

XO: Executive Officer. The second-in-command of a military unit, ship, or aircraft. The XO handles the day-to-day administration and management of the unit while the CO focuses on mission and external relationships.

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