Proprietary software
Proprietary software, as defined by the Free Software Foundation, means any software that does not meet the Foundation's criteria for free software. Non-free is a customary designation for software that fails the Debian Free Software Guidelines, which follow the same basic idea of software freedom. Proprietary means that some individual or company holds the exclusive copyrights on a piece of software, at the same time denying other people the access to the software's source code and the right to copy, modify and study the software.
The term proprietary means "privately owned and controlled". Hence software can remain proprietary even when source code is made publicly available, if control over use, distribution, or modification is retained (e.g., the commercial version of SSH.) On the other hand, software is considered non-proprietary once it is released with a license that would permit others to "fork" the software and release their own modified versions without onerous restrictions, even though the copyright may remain in the hands of a single individual. At least in theory, control has been conceded.