In our context, a protocol is simply a set of rules governing the exchange or transmission of data between devices. That’s it. Nothing more. Just a description of the rules so that the rules may be encoded in any way, shape, or form.
The Internet Protocol (IP) for example describes a specific way to route data, indicating its source and its destination. And Simple Mail Transfer Protocol (SMTP) describes how email can be created, sent, and received.
When exclusive use is claimed for a protocol, it is referred to as a proprietary protocol. By definition, open source software cannot rely in any way on proprietary protocols.
Open protocols underpin the success of both the internet and the web as they can be used by anyone anywhere without permission. (See platform.)