>Proprietary software is another name for nonfree software. In the past we subdivided nonfree software into “semifree software”, which could be modified and redistributed noncommercially, and “proprietary software”, which could not be. But we have dropped that distinction and now use “proprietary software” as synonymous with nonfree software.
>The Free Software Foundation follows the rule that we cannot install any proprietary program on our computers except temporarily for the specific purpose of writing a free replacement for that very program. Aside from that, we feel there is no possible excuse for installing a proprietary program.