The name given in reference works to the home planet of the Vidiians, the Delta Quadrant people ravaged for two thousand years by the disease called the Phage.
Vidiia Prime is the homeworld of the Vidiians as identified in the reference book Star Trek: Star Charts. The name is not spoken in any episode, and the planet is never visited on screen.
The Vidiians are introduced in the Voyager episode Phage. Once known as artists and explorers, they have suffered for some two thousand years from a disease that destroys their bodies. To survive they harvest organs and tissue from other species, which makes their territory a dangerous region for Voyager in its first two seasons.
Episodes such as Faces and Lifesigns explore their society through the scientist Sulan and the doctor Danara Pel. In Think Tank a hologram claims that the Phage has finally been cured.