Definition
The local atmospheric pressure value, expressed in inches of mercury (or hectopascals), that a pilot enters into the altimeter's setting window so the instrument displays altitude correctly relative to mean sea level.
Plain English
A pressure number, given by ATC or a weather report, that the pilot dials into the altimeter so it shows the right height above sea level.
Context Anchor
You encounter this during preflight cockpit checks when setting the altimeter, and in flight when receiving updated altimeter information from weather reports or air traffic control.
Derivation
From 'barometer,' the instrument that measures atmospheric pressure. The 'setting' is the pressure value being set into the altimeter. Knowing the term refers to a pressure value (not a switch position or a mode) helps clarify what is actually being adjusted.
Why Pilots Care
An incorrect barometric setting produces altitude errors that can lead to terrain collision or loss of required vertical separation from other aircraft.
Grounding Statement
Air pressure changes with weather, so the barometric setting tells the altimeter what the pressure is right now for the area where you are flying.
Intuition Check
Do not read setting as just a general preference or switch position. Here it means a specific air-pressure value set into the altimeter.
Example Sentence 1
Before taxi, the pilot listened to ATIS and dialed the current barometric setting of 30.05 into the altimeter.
Example Sentence 2
After landing at the alternate airport the pilot updated the barometric setting from the ATIS before taxiing in.