The OSI is not the final arbiter of the English language, but this definition is long-settled by the vast majority of people who know about software. For example, many governments (including the US) have definitions of "open source software" written into their laws and regulations, and they all basically agree with the OSI definition.
For example, the US Government's "OMB M-16-21: Federal Source Code Policy" defines "Open Source Software (OSS) as: "Software that can be accessed, used, modified, and shared by anyone. OSS is often distributed under licenses that comply with the definition of “Open Source” provided by the Open Source Initiative (https://opensource.org/osd) and/or that meet the definition of “Free Software” provided by the Free Software Foundation (https://www.gnu.org/philosophy/free-sw.html)." https://obamawhitehouse.archives.gov/sites/default/files/omb...