These are the 4 Freedoms of open source software - which OSE applies to open source hardware and other products in general. These are the freedoms to inspect, use, modify, and sell.
> The freedom to inspect or view. In software, this came from the freedom to study how the program works, and change it to make it do what you wish . Access to the source code is a precondition for this - such as FreeCAD files, text documents, spreadsheets, calculations, instructions, etc.
The freedom to use. Run or otherwise execute the software, product, or process. You may be charged for using the thing. But this is a moot point, because as soon as someone buys it, it can be released for free.
The freedom to modify. This is a big point: making improvements or adaptation is a key to distributing value.
Economic freedom. The freedom to distribute or sell. Freedom distribute copies of your modified versions to others. By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.
TIL
https://wiki.opensourceecology.org/wiki/4_freedoms
https://www.gnu.org/philosophy/free-sw.en.html
https://www.gnu.org/licenses/license-list.html#NonFreeSoftwareLicenses