Monophony

Many synthesisers and specifically most modular synths are monophonic - only one note can be played at a given time, and any new notes will either interrupt the previous or will not trigger until the previous has played.

To play multiple notes which don't cut eachother off and act as true independent voices each with their own controllable parameters polyphony is needed; Polyphony is the ability to play multiple independent voices simultaneously, and requires enough oscillators, envelopes, filters, VCAs and other modules to build an entire voice block for each simultaneous note required. this is expensive and also requires a polyphonic sequencer source to provide multiple independent pitch, gate and other cv's.

A compromise solution is to use Paraphony; Multiple notes or voices can be played, but there will not be true polyphony because the voices are not completely independent due to sharing some common element(s) such as just one filter shaping all voices together.

A solution somewhat further reduced in function is to use "Static Chords"; a way of achieving a degree of pseudo-polypohony for those with no polyphonic control source is to use multiple oscillators tuned to different root notes to provide a 'static chord' - for example, three oscillators tuned to the root, minor third and perfect fifth will produce a minor chord, but these pitch intervals will remain fixed regardless of cv input, the chord only being transposed as the pitch cv is altered.