The term includes veterans who have been separated from the armed forces under honorable conditions and who served on active duty in the armed forces during a war or in a campaign or expedition for which a campaign badge has been authorized or during particular defined periods. The Office of Personnel Management’s VetGuide provides a comprehensive list of campaigns and expeditions which qualify for veterans’ preference. The VetGuide is available at the following internet address: https://www.opm.gov/veterans/html/vgmedal2.asp . The term “preference eligible” also includes disabled veterans. In addition, the mother, spouse, or unmarried widow or widower of certain veterans may qualify as a “preference eligible” under particular circumstances. A retired member of the armed forces is generally excluded from the definition of “preference eligible” unless the individual qualifies as a disabled veteran or retired below the rank of major or its equivalent. 5 U.S.C. § 2108.