Final answer:
Negative gauge pressure indicates a vacuum pressure lower than atmospheric pressure. Gauge pressure is relative to atmospheric pressure and can be negative, but absolute fluid pressure cannot be negative.
Step-by-step explanation:
A negative gage pressure means that a vacuum pressure exists in the measured fluid. In gauge pressure measurements, the reference point is atmospheric pressure; gauge pressure is positive for pressures above atmospheric pressure and negative for pressures below it. Most pressure gauges read zero at atmospheric pressure, so any negative reading would indicate a pressure lower than atmospheric, which is a partial vacuum. It is important to note that while gauge pressure can be negative, absolute pressure in fluids cannot be; since fluids cannot pull, the smallest absolute pressure in a fluid is zero.