Regardless of whether or not the definition is a social construct (like the definition of wrists, waists, or...well...any definition at all, really) the area that people call the ridged band is a shitload of fun.
I mean, if you really want to you can argue that every definition is inherently a social construction, and therefore capable of being deconstructed and dismissed as a human creation and not part of the "real" natural world. Hell, you can even argue that the ideas of "real" and "natural world" are human creations. But that takes all the fun out of life.