A transwarp aperture

A transwarp aperture is the open end of a transwarp conduit through which it can be either accessed, or from which a conduit can be exited. (VOY: "Endgame")

In the 24th century, the Borg maintained a series of six transwarp hubs throughout the galaxy, from which thousands of transwarp apertures could be accessed in all four quadrants. The hub allowed the Collective to deploy vessels nearly anywhere in the galaxy, giving them a decisive tactical advantage.

In 2378, the crew of the USS Voyager put into action a plan to destroy the Borg's entire transwarp network, by destroying a series of the interspatial manifolds which supported the network's structure. Entering an aperture in a hub they discovered in the Delta Quadrant, the crew fired a series of transphasic torpedoes as they traveled through the conduit, destroying the manifolds and setting off a chain reaction that destroyed the hub and collapsed the network. Remaining ahead of the resultant shock wave, the Voyager crew was able to exit an aperture located less than a light year from Earth, moments before it collapsed. (VOY: "Endgame")