Subspace filament

From Memory Alpha, the free Star Trek reference.

A subspace filament is something similar to a "road", a way to reach the subspace while inside a wormhole, for example.

A subspace filament was inadvertently created in 2371, when the Starfleet initiated a joint scientific project with the Bajoran and the Cardassian to establish a trans-wormhole subspace communications relay to make it possible for ships in the Gamma Quadrant to contact home, as well as to provide early warning of any Dominion attack.

The mission was complicated by the approach of a previously-unknown, long-period comet. This comet was infused with silithium, which had the potential to permanently destabilize the wormhole if it interacted with the verteron particles in the passage. Unable to alter the comet's trajectory, a shuttlepod from the USS Defiant used a deflector shield to prevent the comet's material from contaminating the wormhole.

During the transit, trace amounts of silithium inadvertently leaked through the shield. However, the small amounts did not destabilize the wormhole, but instead created a subspace filament inside the wormhole that allowed normal communication between the Alpha and Gamma Quadrants. (DS9: "Destiny")