Virtual Display Device
Virtual display devices are portable devices used aboard Dominion warships, which substitute for the viewscreens found aboard most starships.
There are at least two models: a compact headset (used aboard Jem'Hadar attack ships) and a larger shoulder-mounted version (used aboard Jem'Hadar battle cruisers). Dominion ships are normally equipped with only two display devices: one for the Vorta commander and the other for the Jem'Hadar First.
The virtual display device gives the wearer the ability to view the space around the ship by simply turning his head (or as Elim Garak said, "It's like having a viewscreen inside your brain").
The device itself is designed to be worn by Vorta and Jem'Hadar; when worn by other species, there may be some side effects. Headaches are one symptom experienced by humans after wearing the device for an extended period. Cardassians and Bajorans seem to have no problem wearing the headset. (DS9: "The Ship", "Call to Arms", "A Time to Stand", "Tacking Into the Wind")
