Consensual Reality is the idea that everyone influences what is real and what is not by believing in it. For instance, in the matrix, the awakened mudders can do whatever they believe they can do, like how Neo can dodge bullets and jump from building to building The Tick style.

Mage: The Ascension, a pen and paper RPG uses consensual reality in a much broader way, making it a consensual agreement between all of the people alive, allowing mages to cast spells at the risk of paradox, (That is, a mage can try to animate a tree into a big scary monster, but if it's too unbelievable, reality will come back and smack him upside the head.) The net result of this was that in the middle ages, Magic worked but Science was too unbelievable in those days, so Magic worked and Science didn't. Conversely, in the present day Mage, Magic is much harder to do, and Technology much easier to use. Thus providing a backdrop for The Ascension War, a war fought between factions of mages trying to convince society to believe in whatever a pirticular faction wants them to believe.