Desertion is the abandonment of a military duty or post without permission (a pass, liberty or leave) and is done with the intention of not returning. This contrasts with unauthorized absence (UA) or absence without leave (AWOL ˈeɪwɒl), which are temporary forms of absence.
In the United States Army, United States Air Force, British Armed Forces, Australian Defence Force, New Zealand Defence Force, Singapore Armed Forces and Canadian Armed Forces, military personnel will become AWOL if absent from their post without a valid pass, liberty or leave. The United States Marine Corps, United States Navy, and United States Coast Guard generally refer to this as unauthorized absence. Personnel are dropped from their unit rolls after thirty days and then listed as deserters; however, as a matter of U.S. military law, desertion is not measured by time away from the unit, but rather:
by leaving or remaining absent from their unit, organization, or place of duty, where there has been a determined intent to not return;
if that intent is determined to be to avoid hazardous duty or shirk contractual obligation;
if they enlist or accept an appointment in the same or another branch of service without disclosing the fact that they have not been properly separated from current service.
People who are away for more than thirty days but return voluntarily or indicate a credible intent to return may still be considered AWOL. Those who are away for fewer than thirty days but can credibly be shown to have no intent to return (for example, by joining the armed forces of another country) may nevertheless be tried for desertion. On rare occasions, they may be tried for treason if enough evidence is found.
There are similar concepts to desertion. Missing movement occurs when a member of the armed forces fails to arrive at the appointed time to deploy (or "move out") with their assigned unit, ship, or aircraft. In the United States Armed Forces, this is a violation of the Article 87 of the Uniform Code of Military Justice (UCMJ).