The spaceborne entities were intelligent lifeforms that lived in the vacuum of space and fed on energy. They had the ability to transform themselves into various forms, as well as to manipulate matter.
In 2364, an injured member of this species was captured by the Bandi and forced to transform into Farpoint Station on Deneb IV. Its mate, taking the form of a starship, soon arrived at Deneb IV and attempted to free its companion by attacking the Old Bandi City. After the first entity was freed by the USS Enterprise-D, both beings departed the system for parts unknown. (TNG: "Encounter at Farpoint")
In Orion's Hounds, part of the Star Trek: Titan novel series, the USS Titan under the command of William T. Riker encountered this species again. They were variously referred to as "star-jellies" by the Titan crew and "skymounts" by another species who used them as space-traveling vessels.
These entities appeared in the Star Trek Online mission "Echoes of Light" as the player character and the Lukari captain Kuumaarke discover them while exploring worlds with the Lukari for the first time. Kuumaarke is quite interested in them.