proprietary adj. 1. In marketroid-speak, superior; implies a product imbued with exclusive magic by the unmatched brilliance of the company's own hardware or software designers. 2. In the language of hackers and users, inferior; implies a product not conforming to open-systems standards, and thus one that puts the customer at the mercy of a vendor able to gouge freely on service and upgrade charges after the initial sale has locked the customer in.