Subspace sandbar

From Memory Alpha, the free Star Trek reference.

"Subspace sandbar" was a nickname for a type of subspace layer.

Throughout the region of a "sandbar" layer, the barrier between normal space and subspace was unstable. This instability caused gravimetric forces similar to tractor beams to halt any ship from moving through it. The instability also disrupted warp fields and caused disruptions to the power flow of the starships control systems. The edge of the sandbar was called a subspace boundary. A layer of this kind could be exited by a starship with impulse drive.

In 2375, the USS Voyager became stranded in a subspace sandbar in the Delta Quadrant. This sandbar was an intersection point to a trans-dimensional realm. The trans-dimensional distortion portals inside the ship, linking it to this realm, were keeping the the ship in place. Photonic charges fired through the portals, inside Voyager, caused the portal distortions to grow larger and pull the ship deeper into subspace. After the portals were closed the ship realigned itself with normal space, making escape from the sandbar with impulse drive possible. (VOY: "Bride of Chaotica!")