Sparky,
When referring to QNH or sea level etc. then we use the word altitude.
When referring to QFE or distance above a fixed datum then we use the word height.
Controlled airspace surrounding a civilian airfield is always defined by flight level or QNH.
For example, if you flew under East Midlands controlled airspace on the Barnsley regional pressure setting you could potentially bust controlled airspace because you should be flying on the East Midlands QNH and there will usually be a difference between the two.
Regional pressure settings are useful in areas where there is little controlled airspace, for terrain avoidance. Flying cross country in England usually means setting an airfield QNH along the length of the route.
edited to add that I agree with shytorque, but you cannot legally make any sort of instrument approach on regional QNH