AWOL (pronounced "a-wall") is an acronym for the United States and other armed forces expression "Absent WithOut Leave" or "Absence Without Official Leave". The United States Marine Corps and the United States Navy use the term "Unauthorized Absence" (UA) instead. Acronyms and initialisms are abbreviations formed from the initial letter or letters of words, such as NATO and XHTML, and are pronounced in a way that is distinct from the full pronunciation of what the letters stand for. ... The armed forces of a state are its government sponsored defense and fighting forces and organizations. ... United States Marine Corps Emblem The United States Marine Corps (USMC) is a branch of the U.S. military. ...

Military personnel are technically AWOL when they have failed to show up at, or have left, their military assignment without permission, or without a valid pass or leave. These individuals become officially AWOL when they are noted on their unit's morning report as being absent without leave. After 30 days, AWOL individuals are dropped from the unit's rolls and reported for desertion. A pass is permission to be away from ones military unit for a limited period of time. ... In the armed forces, leave is permission to be away from ones unit for a period of time. ... In the United States Army, the morning report is a document produced every morning of the year for every basic unit of the Army, by the unit clerk, detailing personnel changes for the day. ... Desertion is the act of abandoning or withdrawing support from an entity to which one has given an oath, or has claimed to owe allegiance, responsibility or loyalty. ...

Colloquially, the term has now come to characterize anything that is missing or gone; not where it should be. A colloquialism is an informal expression, that is, an expression not used in formal speech or writing. ...

"He made a stupid decision because his common sense went AWOL."

See also

• desertion
• missing movement

The US Navy and Marine Corps use the term Abandoned Post without Cause (APWC) to officially denote a missing service member. My source is the Military.com website. Desertion is the act of abandoning or withdrawing support from an entity to which one has given an oath, or has claimed to owe allegiance, responsibility or loyalty. ... Missing movement refers to the failure of military personnel to arrive at the appointed time to move with a unit, ship, or aircraft; in the United States military, it is a violation of the 87th Article of War. ...