Veteran generally refers to a person who has had long service or experience in a particular occupation or field.
In military context, a veteran is someone who has served in the armed forces, especially during a war.
The term "veteran" can also mean:
1. An experienced person in any profession (e.g. "a 20-year teaching veteran")
2. In American English, specifically refers to former military personnel
3. Sometimes used to describe old, experienced animals (e.g. "a veteran racehorse")