The Prime moon wormhole was a wormhole discovered by the Cardassian explorer Joran Kine.
The wormhole's terminus only opened at certain times and Kine made calculations that would enable his Galor-class shuttle to enter the wormhole, travel to the other side and take readings, before returning through before it closed. He reported his findings, although the scientific minds of Cardassia did not believe him. When others tried to use the wormhole using the same calculations, they were lost and never heard from again, ending Kine's career.
Elim Garak studied the prime moon wormhole while he was at the Bamarren Institute for State Intelligence. (DS9 novel: A Stitch in Time)