Discharge By Purchase

In most contexts bought discharge means discharge by purchase. It is a practice where a soldier pays a fee to be legally released from a contract or service before their agreed term is over. 

While the term is primarily historical, it is still used in certain specific modern or legal contexts. 

In military service buying your discharge colloquially means paying a fine to leave military service. This right is suspended during war time. 

Buying discharge was a corner stone of how professional military, particularly British Army managed their manpower and society heirarchy.  They were separate for ordinary soldier and for officers.

For enlisted men, discharge by purchase was often the only legal way to leave the service before their long term contract. It was a safety valve to recruits who later realise that they were not suited for military life.  In the absence of it they should desert or self-mutilate to get a discharge on medical ground.

In mid 19th century Officers could purchase their ranks like Captain or Major.  When an officer wanted to leave his service he sold his commission to the next person. This served as a pension as the government at that time did not provide pension.

Sergeant Francis Troy of Far From The Madding Crowd uses the money of his wife Bathsheba Everdene to purchase a discharge from the 11th Dragoon Guards.