A kipper is a whole herring

Herring

Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...

, a small, oily fish

Oily fish

Oily fish have oil in their tissues and in the belly cavity around the gut. Their fillets contain up to 30 percent oil, although this figure varies both within and between species...

, that has been split from tail to head, gutted, salted or pickled, and cold smoked.

In the United Kingdom, in Japan, and in some North American regions they are often eaten for breakfast. In the UK, kippers, along with other preserved fish such as the bloater

Bloater (herring)

Bloaters are a type of smoked herring. They are different from the kippers as they are smoked whole, with its innards intact which gives it its unique gamey flavour. The bloater is associated with Great Yarmouth, England; the kipper with Scotland and the Isle of Man...

 and buckling

Buckling (fish)

A buckling is a form of hot-smoked herring similar to the kipper and the bloater. The head and guts are removed but the roe remain. They may be eaten hot or cold.-Origin:...

, were also once commonly enjoyed as a high tea or supper

Supper

Supper is the name for the evening meal in some dialects of English - ordinarily the last meal of the day. Originally, in the Middle Ages, it referred to the lighter meal following dinner, where until the 18th century dinner was invariably eaten as the midday meal.The term is derived from the...

 treat; most popularly with inland and urban working-class populations before World War II.
The English philologist and ethnographer Walter William Skeat

Walter William Skeat

Walter William Skeat , English philologist, was born in London on the 21st of November 1835, and educated at King's College School , Highgate School, and Christ's College, Cambridge, of which he became a fellow in July 1860. His grandsons include the noted palaeographer T. C...

 derives the word from the Old English

Old English language

Old English or Anglo-Saxon is an early form of the English language that was spoken and written by the Anglo-Saxons and their descendants in parts of what are now England and southeastern Scotland between at least the mid-5th century and the mid-12th century...

 kippian, to spawn.