Which communication would suggest that a unit is currently engaged with another task?

The term "Busy" is used in radio communication to indicate that a unit is currently occupied with another task and is unable to respond to additional calls or communications at that moment. This status informs dispatch and other units that they should not attempt to relay messages or assign new tasks to that unit since it is already engaged.

In contrast, a traffic check typically indicates that a unit is actively involved in monitoring a specific situation, but it does not necessarily imply they cannot respond to other communications. "Meet _ at _" suggests a specific location where two units will rendezvous, but it does not convey the message of being unavailable. "In service" indicates that the unit is available for calls and actively on duty, which is the opposite of being engaged with another task. Thus, "Busy" effectively communicates the current engagement status of the unit.