In the course of your adventures, you may run into zones of Wild, or Dead, Magic. Since there have been questions by players, here's the basics of how it works in CD at present.
These are places, large or small, where magic doesn't work right, or work at all. The reasons can vary, but it often has to do with very powerful magics, or places where the gods fought (or died). Places like the Ruins of Myth Drannor, the Helmlands, fallen mythallars, that sort of thing. The Weave is torn, or even burned out, making the use of magic difficult, unpredictable, or sometimes impossible.
Mostly this is something that will impact only higher level dungeons.
Now, a few key things:
Wild Magic works much the same, save that it won't affect existing buffs, only things that are cast, by PCs or NPCs. There is a set value, that can vary by area, of what percentage of spells will turn into a wild surge instead, and produce a totally random result - sometimes good, sometimes bad, sometimes entirely weird.