Mountains are relative, as remarks in this thread illustrate. I grew up with the Cascade and the Olympic Mountains in Washington as my stomping ground, so the foothills in the valleys (that were the size of mountains in places like New England) were hills by comparison. But when I lived places like New York State where the Catskills and other ancient ranges I visited were, as I observed, much lower and not glaciated like the youthful Cascades, it took some perspective to realize that they still needed the respect with which one approaches mountains in general. They do affect the weather, they are places where people can get lost, hurt, or killed. They do the geological and biological work of mountains.

I've lived in Tennessee where the Smokey Mountains are a lot like the western slopes of the Cascades in places, in that they are very wet and so heavily covered with vegetation that climbing is a soggy green bushwhack if you're off of the trail. Here in Texas there are some formidable and much drier mountains in the western side of the state, Guadalupe, and peaks in Big Bend National Park, and beautiful isolated ones like the Davis Mountains (site of McDonald Observatory). Again, biologically these are very important, and you can get yourself into trouble if you don't respect the nature of these mountains.

In south central Oklahoma is a mounded hill called Rainy Mountain. Culturally it is immense to the Kiowa Indians who live in the region and it has been invested with cultural and religious significance that is understood by the local population but probably ignored by outsiders passing through the area. It would be an afternoon walk to the top and back again. Because it stands out by itself, it is a mountain to the eyes of a plains dweller.   

SRS