But I don't think it's terribly useful; there are plenty of things that you could do that the people who coined the term would definitely not agree with.

Instead of inheritance, I could just copy and paste lots of different functions for different types. This would be different than inheritance but I don't think it would count as "composition", and it's certainly not something you should "prefer".

That's fair. I'd agree that isn't composition. I'm not sure the thing you describe is worse than inheritance.... It's not composition though.