What does outbound,inbound mean in aviation ?

Depends on what you are inbound and or outbound for. Are you referring to holding, or the actual approach itself. If its holding you are inbound towards the fix (VOR, intersection NDB) and outbound is after you cross it, the arrow changes directions and you are timing it. Inbound fix for the ILS would be where you intercept the glideslope, and depends on the outbound, most of the time the outbound course wouldn't be for an approach unless you go missed.