Fluidic space is Starfleet and the KDF's designation for the dimension the Undine live in. In contrast to "normal space", there exists no vacuum. Instead the space is filled by omnipresent liquid matter, thus the name "Fluidic space".
Little is known about this dimension. Before 2409 only one incursion of a Starfleet vessel was documented. The U.S.S. Voyager was brought there by the Borg to coerce them into delivering a fatal blow to the Undine, only known by their Borg designation Species 8472 at the time. Before returning to normal space, Voyager indeed had to destroy several Undine ships attacking the intruding vessel, thus laying the foundation for the lasting tensions with this species.
The Undine are not the only species in Fluidic space. At least one cosmozean lifeform known as the Gekli call this dimension its home. Also several lesser lifeforms can be found on "land masses", organic clusters of matter and the equivalent of planets in Fluidic space.
- “Fluid Dynamics”: A Starfleet-KDF-Republic task force commanded by Tuvok and the player enters Fluidic Space to investigate the Borg presence there. They discover the Iconian duplicate ships and destroy a Borg Diamond.
- “Viscous Cycle”: A task force enters fluidic space to destroy Undine Proto-Planet Killers.
- “Mindscape”: The player and Tuvok engage Eric Cooper's command bioship. Cooper is defeated and Tuvok convinces the bioship to leave the Alliance alone.