A mummy is a corpse with exceptionally well preserved skin and dried flesh. This can be due to environmental or artificial means.
On Earth, mummies of Egypt were stored in pyramids. (citation needed • edit)Vulcans practiced mummification as early as the 9th century BC, with the remains of Haadok at P'Jem being one example. (ENT: "The Andorian Incident") The mummified body of the Vulcan Kolinahr master T'Klaas was preserved in the T'Karath Sanctuary. (ENT: "Awakening")
Klingon mummies were identifiable by a particular mummification glyph. (Star Trek IV: The Voyage Home) Some entrepreneurs on Maranga IV claimed to have Molor's mummified head on display for a fee of 50 darseks per person. (TNG: "Firstborn")
In the UK comic strip "Planet of the Dead", the toad-creatures of planet Selkye resembled mummified toads, while in the Gold Key comic "The Mummies of Heitius VII", mummies that acted similar to the Borg were found on Heitius VII.