A health certificate was a legal document issued by a chief medical officer of a space station, which allowed cargo under quarantine for health reasons to be moved elsewhere.
Doctor Julian Bashir was asked to issue a health certificate by Odo in 2373 for the cargo of an Antidean transport that wished to leave Deep Space 9 a day early. It was hoped that the certificate would expedite the ship's departure. (DS9: "Doctor Bashir, I Presume")