Wormholes, also known as Einstein-Rosen bridges, are topological features representing shortcuts between two points in space-time. They can link two points separated by extremely vast distances, such as many light-years. Thus, a wormhole could be regarded as a tunnel, with the two entrances located at different points in space.
To simplify the notion, 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, while the tunnel itself would be 4D.
Wormholes function by tearing traversable holes in space-time and creating a higher spatial tunnel, connecting two points separated by vast distances. To stabilize the tunnel, exotic matter is required, which both the Harvesters and the Sphere have been able to harness. The knowledge required to construct a stable, traversable wormhole was then passed on to humanity by the Sphere as means to uplift humanity to common interstellar travel and achieve leadership within the Resistance.
A wormhole seems to be extremely powerful in terms of gravitational tidal forces and pull, affecting the lunar surface by attracting all dust towards itself. Because of this, travel through wormholes might require a sophisticated resilience shield against the gravitational currents inside the wormhole's throat.
Although wormholes are hard to create and stabilize, they represent the sole type of superluminal travel and thus are indispensable to an interstellar society.