Pressure - Normal force per unit area exerted by a fluid on a containing wall with respect to a reference.
Absolute Pressure - Normal force per unit with respect to zero absolute pressure.
Ambient pressure - The pressure at which a device operate.
Gauge pressure - pressure above or below ambient pressure.
Differential pressure - difference in pressure between any two points in a system.
Total pressure - pressure on a plane normal to the local flow direction
Static pressure - pressure on a plane perpendicular to the local flow direction.
Velocity pressure - net effect of the difference between total pressure and static pressure.