1) A tract or region uncultivated and uninhabited by human beings, 2) An area essentially undisturbed by human activity together with its naturally developed life community
--Definition from Merriam Webster online dictionary
While that definition seems relatively straightforward, it doesn't wholly reflect what Americans have come to understand as wilderness in our own country. And the legal definition as set forth in the Wilderness Act, passed by Congress in 1964 is much more specific in its description of public lands that are to be protected as wilderness.
You might be surprised to learn that the creators of the Wilderness Act weren't thinking only in terms of protecting species and habitats, although that was a big part of it. They loved the idea of being in wild places. They were alarmed by the increasing urbanization and isolation of Americans from their primitive and natural past. They wanted to preserve this as a living museum of what nature and natural worlds look and feel like and they wanted us to have a place to escape from civilization temporarily, to experience solitude and beauty, even risk, in the backcountry. They were truly visionary and their efforts were selfless and bi-partisan.
A good place to begin to understand what it means to set aside as legal, or as we like to say "Big W" Wilderness, is the Wikipedia entry here.
The full text of the Wilderness Act can be read here.
For some FAQs pertaining specifically to proposed Grand Canyon Wilderness, see our page here.