Major was a military rank.
Norman Baker was Head of Security at the Wenley Moor nuclear research facility. (TV: Doctor Who and the Silurians)
Barrington, (TV: The War Games) Daly (TV: Carnival of Monsters) and Popplewell (PROSE: Timewyrm: Exodus) were Majors of the British Army.
Walton (TV: Doctor Who and the Silurians), Alex Cosworth (TV: The Mind of Evil), Beresford (TV: The Seeds of Doom), Husak (TV: Battlefield) and Blake (TV: The Christmas Invasion) were UNIT Majors.
Branwell was a Major in command of the Henlow Downs missile site. (TV: The Invasion)
Rex Butcher was a Major and a writer on an alternate Earth. (PROSE: Atom Bomb Blues)
Ferdinand was the head of security at Mariah Learman's palace. (AUDIO: The Time of the Daleks)
Green was the Major in charge of security on the WOTAN project. (TV: The War Machines)
Alice Hunniford was an American Major. (AUDIO: Renaissance of the Daleks)
Alec Palmer was a Major turned Ghost-Hunter. (TV: Hide)
Shapp was an aide to the Marshal of Atrios. (TV: The Armageddon Factor)
Thessinger was a retired Major and a country landowner in England. (AUDIO: The First Sontarans)
Ian Warne was a Space Corps officer serving under General Nikolai Hermack. (TV: The Space Pirates)
Salateen was an officer in General Chellak's troop on Androzani Minor. (TV: The Caves of Androzani)
Varl was a Sontaran Major who served under Group Marshal Stike. (TV: The Two Doctors)
Skar was a Sontaran Major. (GAME: The Doctor and the Dalek)
Tamasan was promoted to Major sometime after the Battle of Tenacity. (AUDIO: The Lords of Terror)