Final answer:
VFR-on-top allows IFR-rated pilots to fly at VFR altitudes while on an IFR flight plan, giving them the flexibility to select their cruising altitude while maintaining separation from clouds and adhering to VFR rules.
Step-by-step explanation:
VFR-on-top refers to an option available to pilots operating under Instrument Flight Rules (IFR) where they may choose to fly at VFR altitudes rather than the altitudes assigned in their IFR clearance. It is an authorization by Air Traffic Control (ATC) which allows IFR-rated pilots flying IFR to maintain their own separation from clouds while still on an IFR flight plan, providing them with more flexibility in choosing their cruising altitude.
Pilots using the VFR-on-top option must adhere to all VFR rules, such as maintaining a clear distance from clouds and ensuring they are capable of remaining clear of clouds for the duration of their flight. However, they are still responsible for obtaining an amended IFR clearance, if their chosen cruising altitude changes their route or the need arises to descend back into IMC conditions.