If you're absent without permission, you're awol. Your mom may announce she'll be awol from work for the rest of the week, and that you can find her in the backyard lying in the hammock.
When a student is truant from school — simply doesn't show up, with no explanation or excuse — she is awol. Likewise, a volunteer at an animal shelter who skips his weekly shift is awol. This term is actually an acronym, an abbreviation of the military phrase "absent without leave." You'll often see it spelled in all capital letters: AWOL. The term became popular around World War II in the US military, and it caught on with civilians in the 1960s.