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".
Only 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 our dimension, 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 and their humanoid symbionts, the Hylasa call this dimension their home. Also several lesser lifeforms can be found on "land masses", organic clusters of matter and the equivalent of planets in Fluidic space.
 Missions involved
The player will travel to Fluidic space several times during the campaign of the Undine Front.