What signifies a change between phases or between ongoing operations?

The term that signifies a change between phases or between ongoing operations is "Transition." In a joint air operations context, transitions are critical as they mark the shift from one operational phase to another, such as moving from preparation to execution, or altering strategies in response to changing conditions on the battlefield. Effective transitions ensure that forces can adapt and realign their efforts smoothly, maintaining the overall operational tempo and achieving objectives efficiently. This concept is essential for maintaining coherence in operations, not just at the tactical level but also in strategic planning and execution. In contrast, the other options do not encapsulate the specific concept of transitioning between phases in joint operations as clearly.