field of operations

(noun) a region in which active military operations are in progress. Synonyms: field, field of operations, theater, theater of operations, theatre, theatre of operations. Examples: "The army was in the field awaiting action." "He served in the vietnam theater for three years."

(noun) a particular kind of commercial enterprise. Synonyms: field, field of operation, line of business. Example: "They are outstanding in their field."