A kipper is a whole herring that has been split from tail to head, gutted, salted, and cold smoked.
In the UK and the eastern seaboard of North America they are often eaten grilled for breakfast. In the UK kippers, along with other preserved fish such as the bloater, were also once commonly enjoyed as a high tea or supper treat; most popularly with inland and urban working-class populations before World War II.

And now we know. (but I still ain't gonna eat 'em)