"Power under lock and key" definition

Does anyone know what the "power under lock and key" label means for the 7.5 amp fuse shown as being in location F42 in the "Body Computer Fuse Center"? I've searched the manual, and cannot find any other reference to that term or that fuse. Not what it does, not why it's there, not anything!

While the direction for finding that fuse block are frustrating enough, the top notch Engineering that went into the truck should have indicated a much better Manual being written for the consumer. Unfortunately, that is not the case.