Something proprietary is something exclusively owned by someone. Often with connotations meaning it is exclusive and cannot be used by other parties without negotiations.
It may specifically mean that something is covered by one or more patents.
The word proprietary comes from the French word proprietaire from the word in latin proprietarius, which can be compared to the latin word proprietas which means property. Also compare to proprius, which means owned[?].
wikipedia.org dumped 2003-03-17 with terodump