Theater of Operations

Theater of operations – clearly defined geographical area in which a force maneuvers in order to carry out a mission given by the strategic authority. Its limits are defined in the initial joint operation order.
A region in which active military operations are in progress [The free dictionary].
This word was first recorded in 1875–80 [Dictionary.com].
The strategic authority gives a clear geographical area where a force maneuvers to accomplish a mission. Its limits are defined in the initial joint operation order [Балабін & Гардера, p. 270].
An operational area is defined by the geographic combatant commander for the conduct or support of specific military operations. Multiple operations theatres will typically be geographically separate and focused on different missions. Theatres of operations are usually of considerable size, allowing for operations in depth and over extended periods. Also called TO. [Definitions].

Sources:

Українсько-французько-англійський міжвидовий словник з тактики та логістики. Dictionnaire interamées de termes tactiques et logistiques ukrainien-français-anglais: [в 2-х т.] / Київ. нац. ун-т ім. Тараса Шевченка, Військовий ін-т, Центр розробки Доктрини p.651

Балабін, В., Гардера, Р. (2007) Українсько-французько-англійський міжвидовий словник з тактики та логістики. Dictionnaire interamées de termes tactiques et logistiques ukrainien-français-anglais: (в 2-х т.). Київ: нац. ун-т ім. Тараса Шевченка, Військовий

Theate rof operations. (n.d.) The free dictionary. Retrieved from: https://www.thefreedictionary.com/Theater+(warfare)

Theater of operations. Dictionary.com. Retrieved from: https://www.dictionary.com/browse/theater-of-operations

What does Theatre of Operations mean? Definitions. Retrieved from: https://www.definitions.net/definition/Theater+of+Operations