In the Witcher universe Chaos, or "the force", or "power", or "primordial Chaos", is the power which is harnassed and used by mages. Sources are innately sensitive to this magical force but usually unable to master it. Many go mad. The force is said to have become much more prominent in the world after the Conjunction of the Spheres.
Places where Chaos is strongest and most accessible are known as intersections. Strangely, cats are sensitive to these places. Dragons are as well, but as they are considered magical beasts, this seems less strange.
‘The forces of Order, the forces of Chaos. Awfully high-flown words, Borch. You desperately want to position me on one side of the palisade in a conflict, which is generally thought to be perennial, began long before us and will endure long after we’ve gone. On which side does the farrier, shoeing horses, stand? Or our innkeeper, hurrying here with a cauldron of lamb? What, in your opinion, defines the border between Chaos and Order?’‘A very simple thing,’ said Three Jackdaws, and looked him straight in the eye. ‘That which represents Chaos is menace, is the aggressive side. While Order is the side being threatened, in need of protection. In need of a defender. But let us drink. And make a start on the lamb.’