From Royal Archivist Wiki
Throughout the Ingressa exists a measurable force that allows those who can manipulate it to bend or break most of the rules of reality. Although this force manifests differently on each world, it shares a number of common traits throughout the universe that binds all of its myriad forms (sometimes called schools, colleges, paths, or sources) as a single force, known collectively as magic. Those who control and manipulate magic are collectively called mages.
Mana is a resource, slowly renewable but depletable, much like timber. A finite supply of mana exists on each world, and while it usually declines with overuse, it can also regenerate over time. Careful cultivation of magic over generations can increase the amount on a world, but the coordinated foresight and dedication this requires makes it an extremely rare occurrence. For reasons no one can explain (it being magic), mana seems to rapidly decline and not regenerate in the presence of technology powered by electromagnetism. Like electricity, though, mana can be stored in batteries, increased temporarily within a small area with the use of amplifiers, and reduced with the use of dampeners. The magic of some worlds allow its integration with mechanical technology, thus creating a hybrid of mysticism and science commonly called magitech.
Although it exists across much of the known universe, magic rarely travels well from world to world. Much like flora and fauna, every world possesses its own unique version of magical reality. Mana remains largely the same on all worlds, but the ways to manipulate and harness it vary. On many worlds, mages use magic by casting spells. This typically involves performing complex and proscribed rituals to generate specific, well-defined effects. On other worlds, magic appears to be little more than an extension of psionics.
Declining Magic and the Burst: Around 800 years ago, scholars across the Ingressa realized the finite nature of mana when their measurements revealed a sharp decline in mana levels. In the centuries since, the most powerful magical nations, societies, and colleges established regulations on magical use and now try to create more than they use. Most mages, though, do not play by the rules, and scholars watch helplessly as measured mana levels continue to drop.
Roughly 300 years ago, the amount of magic across all of the Ingressa suddenly flared, causing spikes of power that threatened to undo societies accustomed to their lower levels of mana. On many worlds, the Burst, as it is now called, led to mass hysteria and the persecution of those who practiced or were suspected to practice magic.