Altimeter setting is the value of the atmospheric pressure used to adjust the scale of a pressure altimeter so that it indicates the height of an aircraft above a known reference surface.
The setting of a sensitive pressure altimeter is shown in the Kollsman window.
The QNH altimeter setting is one of the data included in METAR messages.
QNH and QFE will have errors when not at station elevation.
QFF is aerodrome pressure (QNH) reduced to sea level.