A Paraphonic synth is a synthesizer which allows you to play multiple notes simultaneously although the notes also share a common signal path.
And unlike a true polyphonic synth in which each of the notes has it's own independent voice architecture, such as filter, envelope and amplifier, the paraphonic synth instead shares a single voice architecture for all notes that are played at once.
What this means is that you can play multiple notes although they will all be affected by the same amplifier and filter settings.
And they also may not be able to sustain independently if a new note is played.
A paraphonic synth has multiple oscillators, each that are capable of producing a separate pitch and all of the oscillator's output is also routed through a single, shared voice architecture, such as a filter, amplifier and envelope.
And because of the shared voice architecture, a paraphonic synth is not considered true polyphonic, as the notes are not able to sustain independently or be affected by different parameters simultaneously.
And many paraphonic synths are also duophonic which means that they allow you to play tow notes at the same time.
Some examples of paraphonic synths include the Korg Poly-800, Moog Subsequent 37 and the ARP Odyssey.