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.
Colloquially, AWOL characterizes something missing or gone; not where it should be. "He made a stupid decision because his common sense went AWOL."