A marine biologist might reasonably talk about an octopus' tentacles, and understand what other people mean when they talk about those tentacles, even though octopuses actually have "arms" in strict terminology.
Similar friction happens with the word "theory" in science or "proof" in mathematics.
But back to the topic: I think enough people use "open source" in a non-rigorous sense that it's worth leaving room for multiple definitions, versus trying to stamp the non-technical ones out. Marine biologists don't generally go around emphatically saying "they're arms, not tentacles!" (well, maybe some do, but mostly in a good-natured, aware-of-how-silly-it-is sense)
Sorry to have tortured your metaphor so much (:
I'd suggest that forums like this are good at being specific about terminology, and rigorous about its application.
In other words you, and others, may have used Open Source incorrectly in the past, and may learn from this thread so you don't I the future.
Perhaps your analogy would better apply to Open Source versus Free Software. That's more akin to octopus and squid. Open Source to commercial is more like talking about tentacles when describing a whale.
Many languages, and especially most subsets of languages in technical use are prescribed; however.
Enough people using literally when they mean figuratively will eventually make literally mean figuratively in casual conversation. But no amount of people saying squid when they mean octopus will make squid mean octopus within the marine biology community.