Earlier quoted context omitted.
The term open source means you have to, at least, have the right to use, modify, and redistribute modifications. It's more than just being able to see the source.
Unfortunately the term "open source" as used by many people is not necessarily synonymous with the official OSI definition available here. The OSI definition is for most intents and purposes equivalent/compatible/similar to the FSF definition of "free (as in freedom) software" available here https://www.gnu.org/philosophy/free-sw.html For an official example of the use of the term "open source" to mean "you can read…
You can complain about ambiguous words and RMS having chosen "free" all you want, but these are the terms we have, and we shouldn't give them up too easily.