>> When did people start taking "open source" as a label seriously?
In the late 90's.
>> The term means nearly nothing in material terms about what you can actually do with the source code.
correct. The term means nothing in and of itself. The license determines what you can do with the code. there are a bunch of licenses that conform to the OSI definition of Open Source. If a company claims to be "open source", but then does not fit the definition of Open Source then they should expect some push-back.
In the late 90's.
>> The term means nearly nothing in material terms about what you can actually do with the source code.
correct. The term means nothing in and of itself. The license determines what you can do with the code. there are a bunch of licenses that conform to the OSI definition of Open Source. If a company claims to be "open source", but then does not fit the definition of Open Source then they should expect some push-back.