Have you served in the US Military? Did you ever serve in a foreign Military? Are you active duty, reserve, or on national guard status? Are you a current student in ROTC, or the Marines OCS program? If the answer is yes, you are Military-Affiliated.
Did a family member or friend(s) serve in the military? Were you involved in their lives before, during, or after? Do you currently volunteer with military or veterans in public service focused efforts? If the answer is yes, you are Military-Affiliated.
The point of the vernacular is to ensure support services and educational opportunities are available to Stanford affiliates who have either a direct or peripheral relationship to military service.