Social construct.

[Belacqua]

So what comprises a mountain exists it doesn't matter what we want to call it, but it's a mountain because people agreed that hills over a certain height are mountains and everyone mostly agreed.

If everyone changed their minds it would change what mountains and hills are.

Where I live, what we classify to be a mountain depends in part on what's around it.

So for example Hijiyama 比治山 (the last character means mountain) is in the center of the city, and it isn't very high. You can walk over it without much effort. One side has a big escalator these days. It just feels mountain-like because it's taller than the buildings around it. On the other hand Fujiyama 富士山 (same character) is a big thing that you have to be serious about hiking up. Nobody would call that a hill. 

So the social construct includes context -- there's a kind of sliding scale. 

I don't think anyone is seriously arguing that the physical object is a creation of society. How we define it, and how we think of it, and how we value it, are all social constructs. No argument there, surely.