Enterprise enters a subspace corridor.
A subspace corridor in the Underspace.
A subspace corridor is a wormhole-like passage through subspace, which allows a starship to travel over great distances in a short time.
In the 21st century, there was a subspace corridor in the Delphic Expanse, extending 11.6 light years from a nebula controlled by the Kovaalans to not far from the Xindi Council planet. In February of 2154, Enterprise used this corridor to travel quickly to the Council planet. (ENT: "E²")
In an alternate timeline, Enterprise traveled through the corridor with a damaged impulse manifold. The particle wake destabilized the corridor, causing it to shift in time. The ship emerged in the year 2037. Fortunately, this was avoided when that Enterprise assisted the 2154 version of the ship in making alterations to the impulse manifold.
There is a vast network of subspace corridors in the Delta Quadrant known as the Underspace. Until their defeat and near-annihilation in the 15th century, the Vaadwaur exploited them for economic and military purposes. The USS Voyager accidentally encountered the Underspace in 2376. (VOY: "Dragon's Teeth")
In 2377, Reginald Barclay speculated that a group of Ferengi may have found either a wormhole or a subspace corridor to bring Voyager to the Alpha Quadrant, before realizing that they were planning to utilize a geodesic fold. (VOY: "Inside Man")