A kipper is a more usually a fillet of smoked mackerel with its shiny skin left on. It is smoked until its flesh is a golden brown. In England and Scotland, kippers are usually served with a garnish of coarsely ground pepper. It’s a strong tasting oily fish, traditionally eaten at breakfast. I think it goes particularly well with scrambled eggs.

Although it’s an archaic term: when you have two fillets (i.e. both halves of the fish) that can be called a “brace of kippers”.