OSC is an extremely popular protocol for sending control commands and parameters between devices and applications. It is a protocol in which there is no confirmation of the data exchange success, that is, the sender doesn't know if the receiver received the data, and the receiver does not know if somebody sent something to it. As a result, data can be lost without any notification to the sender and the receiver. Though, in a local network such a situation is very rare and occurs only if you are using extremely fast frame rates for sending data.
OSC is a thin layer on the UDP protocol. For more information, read about UDP specification.
For using OSC capabilities in openFrameworks projects, you need to use the ofxOsc addon