The term 'sphere of operation' refers to the area in which a person or organization works. This could be a physical area, such as a country or region, or it could refer to a particular field or industry. The crossword solutions for this term are AMBIT (5 letters), ARENA (5 letters), DOMAIN (6 letters), and PROVINCE (8 letters). An AMBIT is a range of authority or activity, an ARENA is a place where activities take place, a DOMAIN is an area of control or influence, and a PROVINCE is a large area of land with its own government. All of these words can be used to describe a sphere of operation.