Like all language, and especially technical or domain-specific language, you need to know your audience/​correspondent well enough to guess which terms are understood in the way you expect, and which ones need clarification. I fully support you, if A is worth the effort to educate. Many As are not.
For this topic, Wikipedia is a reasonable authority and makes it clear that ability to modify/​distribute is a core part of open source as commonly used. Sadly, the Open Source Initiative never got a trademark on it, but has been fighting this fight since the previous milleneum.
Like all language, and especially technical or domain-specific language, you need to know your audience/​correspondent well enough to guess which terms are understood in the way you expect, and which ones need clarification. I fully support you, if A is worth the effort to educate. Many As are not.
For this topic, Wikipedia is a reasonable authority and makes it clear that ability to modify/​distribute is a core part of open source as commonly used. Sadly, the Open Source Initiative never got a trademark on it, but has been fighting this fight since the previous milleneum.