A portal, created through the use of Necromancy that passes from one plane of existence to another.
Often, a necromantic gate will pass through a separate plane to travel quickly from one place in a single plane to another place on the same plane. This is distinct from teleportation, and involves no discomfort for Easterners.
Morrolan's Window is presumed to utilize necromantic gates to allow passage to distant locations and other worlds.