Release is the final stage of the ADSR envelope and results in the sound falling back to silence (zero volts). If using a typical polyphonic synthesizer with keys, the release stage starts when you let go of the key and the time it takes to reach zero is called the release time.
For instance, adjusting the release time to a low setting is going to make your sound drop off suddenly like a staccato effect. The more that you adjust the release to a higher setting, the more graceful the sound will become as it fades out.
With the release set to high, you can change how the sound is played out by deciding where you release the note in the decay stage. With the ADSR graph in mind, the higher or lower you start the release on the graph will determine the volume and length of this last stage.
So with that in mind, releasing soon after the decay stage will give you a long smooth transition into silence. If you wait and release it a later point, the note will start to fade out at a lower volume and will take less time to reach zero.
Using the release stage in the ADSR envelope can bring a lot of character to your sound, creating punchy sounds with less release and more fade-out style sounds with a long release. Like with most functions, play around with the settings and you’ll soon understand the potential!