Variously known as tears, rifts, and doors. Places where one could cross from one world together, including to realms like the Pale Lands, the Feywild, and various realities that were mere bubbles rather than fully-fledged worlds.
Esmund created the Door Jamb to close and redirect the tears, though it was unable to create new ones. The use of it on an already-stressed fabric of reality brought about the Breaking.
Haven’t been seen post-Breaking.