Glossary of Terms:

omni on/poly mode

A MIDI device set to this mode will ignore MIDI channel assignments and respond to all incoming MIDI note data. It will also play multiple simultaneous notes, up to its designed polyphonic limit.

Source: Yamaha: Sound Reinforcement Handbook

Related terms:   MIDI   omni   omni off/mono mode   omni off/poly mode   omni on/mono mode   omni on/poly mode