A mummy is a dead human or an animal whose soft tissues and organs have been preserved by either intentional or accidental exposure to chemicals, extreme cold, very low humidity, or lack of air, so that the recovered body does not decay further if kept in cool and dry conditions. Some authorities restrict the use of the term to bodies deliberately embalmed with chemicals, but the use of the word to cover accidentally desiccated bodies goes back to at least the early 17th century.

Mummies of humans and animals have been found on every continent, both as a result of natural preservation through unusual conditions, and as cultural artifacts. Over one million animal mummies have been found in Egypt, many of which are cats. Many of the Egyptian animal mummies are sacred ibis, and radiocarbon dating suggests the Egyptian ibis mummies that have been analyzed were from a time frame that falls between approximately 450 and 250 BC.

The earliest discovered evidence of deliberate mummification in human cultures now extends to approximately 10,000 B.C. and is documented to have existed across Southeast Asia, China, New Guinea, and Australia in burials discovered there, and is prompting research to cultures documented to 20,000 years ago for evidence of use of the same mummification methods.

In addition to the mummies of ancient Egypt, deliberate mummification was a feature of several ancient cultures in areas of America and Asia with very dry climates. The Spirit Cave mummies of Fallon, Nevada, in North America were accurately dated at more than 9,400 years old. Before this discovery, the oldest known deliberate mummy was a child, one of the Chinchorro mummies found in the Camarones Valley, Chile, which dates around 5050 B.C. The oldest known naturally mummified human corpse is a severed head dated as 6,000 years old, found in 1936 at the Cueva de las Momias in Argentina.

The English word mummy is derived from medieval Latin Mumia, a borrowing of the medieval Arabic word mūmiya (مومياء) which meant an embalmed corpse, as well as the bituminous embalming substance. This word was borrowed from Persian where it meant asphalt, and is derived from the word mūm meaning wax. The meaning of "corpse preserved by desiccation" developed post-medievally. The Medieval English term "mummy" was defined as "medical preparation of the substance of mummies", rather than the entire corpse, with Richard Hakluyt in 1599 AD complaining that "these dead bodies are the Mummy which the Phisistians and Apothecaries doe against our willes make us to swallow". These substances were called mummia.

The Oxford English Dictionary defines a mummy as "the body of a human being or animal embalmed (according to the ancient Egyptian or some analogous method) as a preparation for burial", citing sources from 1615 AD onward. However, Chamber's Cyclopædia and the Victorian zoologist Francis Trevelyan Buckland define a mummy as follows: "A human or animal body desiccated by exposure to sun or air. Also applied to the frozen carcase of an animal imbedded in prehistoric snow".

Wasps of the genus Aleiodes are known as "mummy wasps" because they wrap their caterpillar prey as "mummies".

While interest in the study of mummies dates as far back as Ptolemaic Greece, most structured scientific study began at the beginning of the 20th century. Prior to this, many rediscovered mummies were sold as curiosities or for use in pseudoscientific novelties such as mummia. The first modern scientific examinations of mummies began in 1901, conducted by professors at the English-language Government School of Medicine in Cairo, Egypt. The first X-ray of a mummy came in 1903, when professors Grafton Elliot Smith and Howard Carter used the only X-ray machine in Cairo at the time to examine the mummified body of Thutmose IV. British chemist Alfred Lucas applied chemical analyses to Egyptian mummies during this same period, which returned many results about the types of substances used in embalming. Lucas also made significant contributions to the analysis of Tutankhamun in 1922.