Marrowbone is a type of offal. The shoulder or thigh bones of calves or oxen contains marrow, a soft substance extracted from the bones and then cooked or after cooking extracted and eaten as a delicacy. Marrowbone is used in sauces or stews.
Dowell, P., Bailey, A. (1980) The Book of Ingredients, Dorling Kindersley. ISBN 0718119150.