Like Quatschmacher said it’s a source of voltage that can be used to offset parameters.
A simple example is offsetting an LFO that is modulating a filter. The DC can nudge the LFO over so that the LFO is unipolar and so not effecting the lower end of the filter.
Or let’s say you have a sequence running and want to have one oscillator switch up to a fifth in a performance. Just set the DC to the VCO to bring it up a fifth in the mod matrix but then turn amount to 0. In the sequencer route a mod lane to that Mod Amount to 100%. Now run that sequence and you’ll hear it play with that VCO up a fifth. Then mute that lane when you want it to go back to the tonic. Since it’s voltage and not just MIDI notes you can also vary amount per step of the sequencer for that old school analog sequencer sound where you had to dial in notes by ear-hand and get some slightly off notes.
It’s a fixed offset. For example you might want to push an oscillator into a particular spot in the stereo field so you’d apply DC as source and Pan as destination.
Just to be clear: This would be pushing the whole audio signal in the stereo field not just the oscillator since there is just one filter that the oscillators go into and panning is post filter.