Other forms: AWOLS; AWOLs
In the military, someone is considered AWOL if they leave their post without a superior's official permission. And you'll be AWOL, too, if you don't show up after promising to help out at your little brother's birthday party.
AWOL is a military acronym that stands for "absent without leave." In the Army or Navy, being AWOL is not as serious as desertion (which is when a person leaves with no intention of returning). If someone is AWOL, they've only neglected their duties for a short period of time. Used in a nonmilitary context, being AWOL means not showing up when you're expected to: "We don't have a math teacher today because the substitute seems to be AWOL!"