Magic

In Game Glossary
"Magic is the art of bending the power of Chaos to one's will. Practitioners of the art must master a vast and complicated corpus of knowledge and, it seems, women have a special predisposition for it. Sorcerers seek out talented children and teach them.

The Power bound in spell formulae may be used for healing, teleportation, destruction, creating illusions, and altering form. The most famous spells are named after their creators, e.g. Alzur's Thunder of Merigold's Hailstorm. Thanks to magic, it is also possible to create magical glyphs and amulets, such as the witchers' medallions.

The witchers' Signs are very simple spells, mostly kinetic or mind-influencing. To use them, one needs concentrated will and a hand gesture. Casting Signs is not time-consuming, so witchers use them when fighting monsters.

Magically gifted children are born all over the world. They are called Sources. The Brotherhood of Sorcerers was charged with finding and training such children. Descendants of Lara Dorren are a special case - their magical gifts are very strong. They can travel through time and space, and release the pure energy of Chaos. These powers are wild and difficult to control, though, and are activated in moments of stress, often surprising their possessor.

The power used to cast spells is drawn from the elements. Fire is the best but simultaneously most dangerous elemental source. Mages who specialize in the magic of fire often achieve great power, but they pay a price for it: as fire addicts, they often suffer burns or even die engulfed in flames. The essence of fire becomes their essence, which makes them vulnerable to water."

Learned via multiple sources, including but not limited to An Invitation to Magic and The Conjunction of the Spheres.