Absolute Pressure: Gage pressure plus atmospheric pressure.
Absolute Zero: Temperature at which thermal energy is at a minimum. Defined as 0 Kelvin, calculated to be -273.15°C or -459.67°F.
ac: Alternating current; an electric current that reverses its direction at regularly recurring intervals.
Acceleration: A change in the velocity of a body or particle with respect to time. The parameter that an accelerometer measures (dv/dt). Units expressed in "g".