Gauge pressure is the pressure you read on the gauge, which typically aren't 'zeroed' out. When measuring pressure, gauges don't usually account for the pressure of the air. So let's say you have a gauge attached to your car tire and it reads 18psi. That means the pressure in the tire is 18psi above air pressure, which (IIRC) is ~14.7psi) so the actual pressure in the tire is 18psi + 14.7psi = 32.7psi. 32.7psi is the absolute pressure, because it measures from zero pressure, while 18psi is the gauge pressure, because it measures with the 'zero' taken to be the ambient air pressure.
In this case, it would be silly to use 1psi absolute pressure as it would mean the tank is in partial vacuum and would require some serious plumbing to get the gas out of it (or air would back up into the tank and make the rocket inoperable). However, there was so little information in the question that I had to ask.