OSC Open Sound Control

OSC is a communication protocol (like MIDI).
"Open Sound Control is just about the worse possible name for a protocol since I'd thought for a long time that this protocol could only be used to control sounds. Nothing is further from the truth. OSC should be renamed OAC – Open Anything Control - which would be a far better name since it can be used to control *anything* " (Joe Armstrong)

OSC allows devices like digital mixers, light boards, tablet apps, other software to talk to each other. Unlike MIDI, it has an unlimited number of commands it can understand and act upon as long as the device or software you are using understands OSC
Each manufacturer will devise a set of specific OSC commands which their device will understand and respond to. They often publish a document detailing all the available commands that can be utilised.
Unlike MIDI, you don't need an interface. OSC can communicate over wifi and works when all devices are on the same network.