Wild Magic, as its name suggests, is a form of magic that is exceptionally chaotic and unpredictable. Whether it is the natural state of magic before being refined and focused by various means, or it is magic that has been deliberately made unstable by some external factor, wild magic is an erratic power that can potentially hold salvation or damnation, depending on your luck.
This form of magic has made repeated appearances in Dungeons & Dragons. Practitioners of wild magic are commonly referred to as Wild Mages, stemming from the name of the original kits from Advanced Dungeons & Dragons.
In the Forgotten Realms, so-called "Wild Zones" are places where the natural flow of magic has been corrupted, causing all magic within that area to become wild magic. These places are also known as Helmlands, a taunt to the God of Guardians who inadvertently created them when he smote the Goddess of Magic, Mystra.
"Spellscar Magic" is a unique strain of semi-wild magic unleashed by the effects of the Spellplague.