The Centering is a term used by scholars of religion, history, geography, and the arcane. It refers to the power of the here and now. As events become more remote in their time or geography, they are known to become more vague, mythic, and in some case, unreal. There is some speculation that, because of the powers unleashed by Aversill in opening the Trods, reality, it’s place and time, are unhinged. Thus, the universe is as ruled by myth as it is by logic. The gods are rivalled by Loa who seem to have no relgion. Great heroes become gods and entire empires seem to spring up out of nowhere. On the map, regions may seem tiny, and yet, travel time through these regions can double, triple, or even quadruple expectations. There are tales of caravans emerging from the Aradat Wastes decades late having, according to the caravan drivers, only been gone for a week. At a certain point, geography becomes arcana, and history becomes religion. Getting lost in the wastelands in the world runs the risk of simply disappearing.
Not every race can center. Humans can, for instance. Eladrin cannot. Any creature whose home is another plane such as the Fey Wyld or the Shadowfell cannot center. Any creatuere with an unnatural origin (especially abberrants) cannot center. Thus, it is not possible for, say, a group of Genasi to build a civilization in the real world that is centered. Instead, it is prone to the dangers of fading.
The Fade is the opposite of the Center. The Fade (or fading), as a term, refers to locations or events that have lost or are in the process of losing their stable reality. Thus, a ruin that was once geographically stable migh fade over the years into a trod opening onto some plain of ruins (and thus become much more dangerous and large). Often, adventurers and explorers refer to their journeys as going into the fade.
There may be some concern amongst adventurers which is worse, a faded geography or a centered geography. For instance, among the creatures who can center are Humans, Dwarves, Halflings, Half-orcs, and Half-elves. At the same time, Orcs can center, as can Kobolds, Goblinoids, and perhaps worst of all, Dragons. Kingdoms with a nearby ruin then are wont to clear the territory of their most fearsome mundane enemies lest the place fade into a Trod for some distant and horrible place.
Centered individuals sometimes, themselves, fade from prolonged exposure to the unrealities of the various wastelands and uninhabited reaches of Allusia. These people are referred to as the Fringe or are said to be living on the Fringe. Either way, it suggests a condition where Fade and fading realities have become more native than the Center and centered realities. The result is anti-social attitudes, xenophobia, and feelings of angst associated with entering civilization. A hero on the fringe might send runners into small villages to keep up contact, but if their life on the fringe has become total, they may find it impossible to be among villagers.