The "subspace seaweed" retrieved from the interphase pocket
A subspace interphase pocket or subspace pocket is a self-contained region of subspace.
In 2370, the runabout USS Mekong, piloted by Lieutenant Jadzia Dax and Arjin, collided with a subspace interphase pocket in the Gamma Quadrant. After recovering from the stability loss, they found they had picked up an unknown mass, termed "subspace seaweed" by Dax, that had become embedded in the runabout's starboard nacelle. After bringing the mass back to Deep Space 9, it was discovered that it was in fact a protouniverse undergoing accelerated development. As the growth of the protouniverse threatened the station, Dax and Arjin transported it back to the Gamma Quadrant and deposited it back in the subspace pocket. (DS9: "Playing God")
In 2375, USS Voyager discovered a subspace sinkhole in the Delta Quadrant that had pulled in one of its shuttlecraft. The sinkhole led to a pocket of subspace that contained an entire star system consisting of a G-type star and three planets. There was a temporal differential between the pocket and the rest of the universe of 0.4744 seconds per minute. The pocket collapsed, crushing everything inside, when the sinkhole was sealed by Renovation Team Nova. (VOY: "Gravity")