What refers to the distance the wingman must maintain while being out of the lead's jet wash?

The correct choice pertains to the concept of visual reference criteria, which establishes the necessary distance a wingman must maintain to ensure safety and effective formation flying. This distance is crucial because being in the lead's jet wash can significantly affect the wingman’s ability to maneuver and maintain control of their aircraft. The visual reference criteria provide guidelines that help pilots gauge their positioning relative to the lead aircraft, ensuring they stay clear of turbulent airflows that could lead to loss of control or instability.

In contrast to the correct answer, the other options do not specifically address the required distance from the lead's jet wash. Jet wash maneuvering is not a standard term used in aviation to describe this situation, and while safe flying distance suggests a level of safety, it lacks the specific context of maintaining visual reference for effective flying in formation. Clearance guidelines typically apply to airspace and operational regulations rather than to aircraft positioning in formation flying. Thus, visual reference criteria is the most accurate term that encapsulates the need for maintaining proper distance to avoid adverse effects from the lead aircraft's jet wash.