Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the pressure relative to the ambient pressure.
Mercury column
The effects of an external pressure of 700 bar on an aluminum cylinder with 5 mm (0.197 in) wall thickness
Water escapes at high speed from a damaged hydrant that contains water at high pressure (due to high pressure of the water it behaves like it is sprayed)
Low-pressure chamber in Bundesleistungszentrum Kienbaum, Germany
Atmospheric pressure, also known as air pressure or barometric pressure, is the pressure within the atmosphere of Earth. The standard atmosphere is a unit of pressure defined as 101.325 kPa, which is
Pressure
…This is one example of a practical application of pressure. For gases, pressure is sometimes measured not as an absolute pressure, but relative to atmospheric pressure; such measurements are called gauge pressure. An example of this is the air pressure in an automobile tire, which might be said to be "220 kPa (32…
Kollsman-type barometric aircraft altimeter
Cloud formation above Snæfellsjökull (Iceland), formed above the mountain by orographic lift
Hurricane Wilma on 19 October 2005. The pressure in the eye of the storm was 882 hPa (12.79 psi) at the time the image was taken.