Weave

The Weave is an essential element of the universe, running through everything in unseen threads. Some creatures, objects, and locations have deep, intrinsic ties to the Weave and can perform extraordinary feats that come naturally to them (a beholder’s flight, a vampire’s charming gaze, a dragon’s breath weapon, and so forth). Creatures with the necessary talent and skill can also manipulate the Weave to perform magic by casting spells.
The Weave isn’t normally visible or detectable, even through the use of spells. Detect magic doesn’t let you perceive the Weave, for instance. The Weave isn’t magic, precisely, any more than a collection of threads is a garment; it’s the raw material from which the tapestry of magic is woven.
In two senses, both the metaphorical and the real, the goddess Mystra is the Weave. She is its keeper and tender, but all three times the goddess of magic has died or been separated from her divinity (twice as Mystra, and once as her predecessor, Mystryl), magic has been twisted or has failed entirely. With Mystra’s last death and the coming of the Spellplague, the Weave was thought destroyed, and the term lost its significance. Since the end of the most recent Sundering, both Mystra and the Weave have returned to their roles of centuries past, and spells and Magic Items are more reliable than they had been while the Spellplague raged.