Well, you'd be wrong: https://www.merriam-webster.com/dictionary/open-source

In case you don't know, the dictionary doesn't prescribe meaning, it catalogs the commonly accepted usage of a word. That's why it listed "literally" to mean "figuratively", because along the way, people started using "literally" to mean "figuratively", so that's the definition now.

The common definition of open source does not match the OSI definition...

> people generally use “shared source” or something

"Shared source" was a Microsoft license and not at all generally accepted by anyone. A quick Google search found no references to this term used to describe open source.