Sir, I will take a shot at that, and I'm sure my colleagues might want to weigh in.
The simple definition is that anyone who has served in the military for any period of time is a veteran, but that doesn't necessarily mean they qualify for the various benefits that we administer in the Department of Veterans Affairs. Because our benefit programs, our health care programs, and our national cemetery administration programs were developed over time in a piecemeal fashion based on statutory changes provided by our Congress, there is not even uniformity within our own Department of Veterans Affairs.
For example, if you serve during a period of war, you can qualify for many benefits after 90 days of service. But if you are disabled on your first day of military service, you can also become qualified for most VA benefits based on one day of service. If you served in peacetime, sometimes you require two years of military service or the full term for which you are called to active duty to qualify for the benefit.
I think you can see that there is no simple definition of what a veteran is for the purposes of qualifying for the benefits that we administer.