A term that designates ownership, often related to trade secrets or otherwise restricted access for the general populace. The opposite of this is open – for example, open-source software makes its entire code available for anyone to see and modify, even to use in their own project.
This isn’t possible for proprietary code – in fact, it would be illegal. Lots of software, hardware and firmware creators choose to keep their work proprietary, to avoid espionage and theft of intellectual property.