The Flight Path Vector (FPV) is a bit hard to say in the cockpit, so it is referred to as "The Bird", and looks thus:
When The HDG V/S – TRK FPA pushbutton on the Flight Control Unit (FCU - i.e. the autopilot control panel) is pushed, the flight director, normally either cross bars or V-bars (depending on customer option), is replaced by the Flight Path Director (FPD), a symbol which looks like a set of extended wings.
The pilot's task is then to fly the FPV onto the FPD bars, so that they look like one symbol:
Calling the FPV "caged" isn't a term I have heard is this respect, but may be a colloquial term in some companies.