Personally, a Veteran is anyone who put on the uniform and either still serves or has received a Honorable discharge DD-214.
Federal job preference is for those honorable separated veterans (this means an honorable or general discharge) who served on active duty (not active duty for training) in the Armed Forces:
during any war (this means a war declared by Congress, the last of which was World War II).
For more than 180 consecutive days, any part of which occurred after 1/31/55 and before 10/15/76.
During the period April 28, 1952, through July 1, 1955 (Korean War).
In a campaign or expedition for which a campaign medal has been authorized, such as El Salvador, Lebanon, Granada, Panama, Southwest Asia, Somalia, and Haiti.
those honorably separated veterans who 1) qualify as disabled veterans because they have served on active duty in the Armed Forces at any time and have a present service-connected disability or are receiving compensation, disability retirement benefits, or pension from the military or the Department of Veterans Affairs; or 2) are Purple Heart recipients.
Campaign Medal holders and Gulf War veterans who originally enlisted after September 7, 1980, or entered on active duty on or after October 14, 1982, without having previously completed 24 months of continuous active duty, must have served continuously for 24 months or the full period called or ordered to active duty.
http://usmilitary.about.com/od/benefits/a/vetbenefits.htm