Reserve can also imply the type of commissioning. Yrs ago ROTC grads received a "reserve" commissioning and did not get a "full" commissioning for several yrs, usually around the 7 yr marker. SA grads received a "full" upon graduation
What this meant to them was if there was a RIF, they were not safe. The military would be required to release them prior to hitting the "full" commission officers.
For many gung-ho kids, this was a real recruitment tool for an SA, knowing that they were safe, especially in 93-94 when the AF RIFd 95% of the Active Duty Reserve Commissioning for class of 85 and 86. There were pilots who had yet to complete their payback and were cut.
I believe the rule has changed yrs ago, and now all SA cadets are like ROTC, they do not receive "full" anymore.
Now what does that mean for your job...nothing, you are still ACTIVE DUTY for your commitment purposes. You can stay pass the 5 yr marker and still serve Active.
Bullet who retired 18 mos ago still has 3 1/2 yrs left on his reserve commitment. YEP, they can call him back, but like others stated "in active" means nothing more than before we go to a draft situation, we will grab you. This is why many military members laugh at the thought of the draft ever returning. He does not do weekends or reports to the military at all, but they have the ability to call him back anytime they want, no questions asked, he will be required to report.