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.

Polyphony: multiple independent voices simultaneously.

Paraphony: multiple notes or voices but not 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.

Static Chords: A solution, though somewhat reduced in function, to achieve 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.