A wormhole or "Einstein-Rosen bridge" is a hypothetical topological feature that would fundamentally be a shortcut connecting two separate points in spacetime. A wormhole may connect extremely long distances such as a billion light years or more, short distances such as a few feet, different universes, and different points in time.
A wormhole is much like a tunnel with two ends, each at separate points in spacetime. For a simplified notion of a wormhole, space can be visualized as a two-dimensional (2D) surface. In this case, a wormhole would appear as a hole in that surface, lead into a 3D tube (the inside surface of a cylinder), then re-emerge at another location on the 2D surface with a hole similar to the entrance. An actual wormhole would be analogous to this, but with the spatial dimensions raised by one. For example, instead of circular holes on a 2D plane, the entry and exit points could be visualized as spheres in 3D space.
Discovery of stable wormholes connecting some star systems resulted in a quantum shift in the development of the WWU. Once transiting these features--first via robotic drones then eventually by manned vessels--become possible, different colonies near them began to interact to a much greater degree.
Believed to exist in abundance in the quantum foam, and that they appear and disappear spontaneously at the Planck scale, stable versions of such wormholes were considered as dark matter candidates.
It is believed that with enough study and science, humanity could eventually control the brane of space in such a way as to create artificial wormholes.