What does the term "crossfeed" refer to in aircraft fuel systems?

The term "crossfeed" in aircraft fuel systems specifically refers to the ability to transfer fuel between tanks. This functionality allows for balancing fuel loads by moving fuel from one tank to another to optimize the aircraft's center of gravity and overall performance. Crossfeeding can also ensure that fuel is available to the engines from different sources within the aircraft, especially in situations where a particular tank may be depleted or compromised.

The other options do not accurately capture the definition of "crossfeed." For example, the process of refueling in flight refers to a different operation entirely and is commonly known as air-to-air refueling. Indicating fuel levels pertains to measurement systems that display how much fuel is in each tank, while regulating fuel flow to engines involves controlling the amount of fuel being delivered to the engines, which is also distinct from the concept of crossfeeding. Thus, the distinction lies in the specific capability of transferring fuel between tanks, which ensures efficient fuel management in flight operations.