Absolute pressure

Gauge pressure plus atmospheric pressure.

The pressure of the atmosphere on a surface. At sea level, a pressure gauge with no external pressure added will read 0 psig. The atmospheric press is 14.7 psia (again, at sea level). If the gauge pressure (psig) reads 15 psig, the absolute pressure (psia) will be 15 + 14.7, or 29.7 psia.


Source: Handbook of water and wastewater treatment plant operations

Wikipedia:  https://en.wikipedia.org/wiki/Pressure_measurement#Absolute