it means giving up (flipping a switch) throtle control to the ESC's governor so that your left stick only controls the blade angle aka altitude. the heli will be at 'full throtle' until you flip that switch.

i fly in idle up 100% of the time. take off, hovering, landing, etc. means when i land it's at full throtle and half stick instead of zero stick. to shut it down i flip the switch. hovering occurs at 66-75% stick.