What term indicates that a unit is currently engaged and unavailable?

The term "Busy" is the correct choice as it specifically indicates that a unit is currently involved in a call or another duty and therefore unavailable for additional assignments. In the context of emergency services, being busy means that the unit is actively occupied with a situation that requires their attention, and they cannot respond to other calls or incidents at that moment.

This terminology is critical for effective communication and management of resources within emergency services, ensuring that dispatchers and other units are aware of the current status and availability of their colleagues. The term allows for better coordination, as it prevents multiple units from being sent to the same incident when one is already engaged.

Other options, like "Out of Service," typically refer to a unit that is temporarily unable to operate due to maintenance or other reasons, while "Out of Service / Subject to Call" implies a specific condition that might allow for re-engagement under suitable circumstances. "In Service" indicates that a unit is actively available and ready to respond. Knowing the distinctions between these terms helps in understanding overall unit management and operational readiness in law enforcement contexts.