A whaleback was a type of cargo steamship of unusual design, with a hull that continuously curved above the waterline from vertical to horizontal. When fully loaded, only the rounded portion of the hull (the "whaleback" proper) could be seen above the waterline. With sides curved in towards the ends, it had a spoon bow and a very convex upper deck. It was formerly used on the Great Lakes of Canada and the United States, notably for carrying grain or ore. The sole surviving ship of the "whaleback" design is the SS Meteor, which is docked in Superior, Wisconsin as a museum ship.

The term developed in common usage in response to the ship's appearance when fully loaded. A total of 44 such vessels were constructed from 1887 to 1898. All but two were built initially as lake freighters for service on the Great Lakes. Six were built at Duluth, Minnesota; 33 were built at West Superior, Wisconsin; 2 at Brooklyn, New York; one at Everett, Washington; and one at Sunderland, England. A number of the Great Lakes vessels left the lakes for service on saltwater seas.

The term "whaleback" has also been applied to a type of high speed launch first designed for the Royal Air Force during World War II, and to certain smaller rescue and research vessels especially in Europe that, like the Great Lakes vessels, have hulls that curve over to meet the deck. An example of the former is the British Power Boat Company Type Two 63 ft HSL. The designation in this case comes not from the curve along the gunwale, but from the fore and aft arch in the deck.

Another application of the term is to a sheltered portion of the forward deck on certain British fishing boats. It is designed, in part, so that water taken over the bow is more easily shed over the sides. The feature has been incorporated into some pleasure craft based on the hull design of older whaling boats, in which it becomes a "whaleback deck".