What is Tonsure?

Legal Definition
Tonsure /ˈtɒnʃər/ is the practice of cutting or shaving some or all of the hair on the scalp, as a sign of religious devotion or humility. The term originates from the Latin word tōnsūra (meaning "clipping" or "shearing") and referred to a specific practice in medieval Catholicism, abandoned by papal order in 1972. Current usage more generally refers to cutting or shaving for monks, devotees, or mystics of any religion as a symbol of their renunciation of worldly fashion and esteem. Tonsure also refers to the secular practice of shaving all or part of the scalp to show support or sympathy, or to designate mourning.

Tonsure is still a traditional practice in Catholicism by specific religious orders (with papal permission). It is also commonly used in the Eastern Orthodox Church for newly baptized members and is frequently used for Buddhist novices and monks. It exists as a traditional practice in Islam after completion of the hajj and is also practiced by a number of Hindu religious orders.
-- Wikipedia
Legal Definition
In old English law. A being shaven; the having the head shaven; a shaven head. 4 Bl. Comm. 367.
-- Black's Law Dictionary
Legal Definition
The shaving of the hair from the crown of the head.
-- Ballentine's Law Dictionary