Magic

The weave, controlled by Mystra, the goddess of magic, is the way in which spellcasters can manipulate and access the raw magics of the world. To most the weave is an intangible force spreading throughout almost all corners of the world. This is the same for casters utilising the arcane, divine or the natural essence of the worlds magic. If Mystra or the weave itself were to be stressed immensely either wild magic or dead magic zones could be created. There are ways in which mortals can temporarily or permanently restore these zones, however it is not without great cost or direct assistance from Mystra herself. Those chosen by Mystra are gifted with Spellfire, the ability to absorb any magic cast towards them and convert it to raw magical energy and release in a myriad number of ways. 
Casting magic causes a knot to form in the weave as the essence is manipulated into doing as the caster desires, zones of wild magic will often create an extra knot, a more complicated knot or sometimes even undo the knot itself. Even if one exercises tremendous control and care in their casting, the weave has almost a mind of its own and works its own desires. Cast with care...
Dead magic zones exist where there has been immense stress on the weave, to the point where the threads are no longer there. No magic can be cast in or into these areas as there is nothing to manipulate. In areas such as these strange flora and fauna may flourish, i.e plants growing within a dead magic zone may inherit magic resistant or magic immune properties.