Haggis is a Scottish sausage. Haggis is made from liver, lungs and heart of sheep, chopped with onions, otameal, parsley and seasonings. This mixture is stuffed into a paunch which is traditionally sheep's stomach. Haggis needs a long cooking, but commercially available ones have been pre-cooked and so need a 30 minutes steaming or baking, or a quick zap in the microwave.
Dowell, P., Bailey, A. (1980) The Book of Ingredients, Dorling Kindersley. ISBN 0718119150.