The Webway, or Labyrinth Dimension, is an extra-dimensional space created by the Old Ones in the Warhammer 40k Universe.
It is used by the Aeldari for faster-than-light travel. It is an incredibly complex network of arteries and capillaries, a maze of glowing tunnels, and a mystic tapestry of hidden threads that spread across the veil between realspace (4d spacetime continuum) and warpspace (the hyper-dimensional plane composed entirely of psychic energy that underlies the physical universe).