Plain English Meaning
How heavily the air is pressing down at a particular place and height. The higher you go, the less air is above you, so the pressure drops.
Full Definition
The pressures exerted by the weight of the atmosphere at a given location and altitude, typically measured in inches of mercury (in Hg) or hectopascals (hPa). Barometric pressure decreases as altitude increases, and varies with weather systems at any given altitude.
Context Anchor
Seen in high-altitude flight, cabin pressure, altimeter setting, weather, and altitude-induced decompression sickness discussions.
Derivation
From the Greek 'baros' meaning 'weight,' combined with 'metric' (measure). A literally measures the weight of the atmosphere pressing down on a .