There are two places to look to find what absences should be excused: state rules and local district policies.
There are State Rules that apply in all school districts, and they list several types of absences that are excused. You can find the current state rules online, and the section that says what absences are excused is at WAC 392-401-020, here: https://apps.leg.wa.gov/wac/default.aspx?cite=392-401-020.
Excused absences include reasons like illness or health condition, family emergency, and absences due to safety concerns. Those are just some examples. Check the full list if you have questions about whether a particular absence should be excused.
Also check your own school district’s policy on attendance. Districts must follow the state rules and excuse absences that are on the state list. They can also add to that list if there are additional reasons that they would excuse an absence.
The state rules sometimes change, so it is a good idea to check them directly if you have questions about the kinds of absences that should be excused.
If the reason for an absence is not on the excused list, then it would be "unexcused."