The barometric altimeter setting which will cause the altimeter to read airfield elevation when on the airfield. In ISA temperature conditions the altimeter will read altitude above mean sea level in the vicinity of the airfield
QFE
The barometric altimeter setting which will cause an altimeter to read zero when at the reference datum of a particular airfield (generally a runway threshold). In ISA temperature conditions the altimeter will read height above the datum in the vicinity of the airfield.
QFE and QNH are arbitrary Q codes rather than abbreviations, but the mnemonics "Nautical Height" (for QNH) and "Field Elevation" (for QFE) are often used by pilots to distinguish them.