Porpoises ( /ˈpɔrpəs/; also called mereswine) are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen. The most obvious visible difference between the two groups is that porpoises have shorter beaks and flattened, spade-shaped teeth distinct from the conical teeth of dolphins.

The name derives from French pourpois, originally from Medieval Latin porcopiscus (porcus pig + piscus fish).

Porpoises, divided into six species, live in all oceans, and mostly near the shore. Freshwater populations of the finless porpoise also exist. Probably the best known species is the harbour porpoise, which can be found across the Northern Hemisphere. Like all toothed whales, porpoises are predators, using sounds (echolocation in sonar form) to locate prey and to coordinate with others. They hunt fish, squid, and crustaceans.

Porpoises, along with whales and dolphins, are descendants of land-living ungulates (hoofed animals) that first entered the oceans around 50 million years ago (Mya). During the Miocene (23 to 5 Mya), mammals were fairly modern. The cetaceans diversified, and fossil evidence suggests porpoises and dolphins diverged from their last common ancestor around 15 Mya. The oldest fossils are known from the shallow seas around the North Pacific, with animals spreading to the European coasts and Southern Hemisphere only much later, during the Pliocene.

Walter Mitty is a fictional character in James Thurber's short story "The Secret Life of Walter Mitty", first published in The New Yorker on March 18, 1939, and in book form in My World and Welcome to It in 1942. It was made into a film in 1947.

Mitty is a meek, mild man with a vivid fantasy life: in a few dozen paragraphs he imagines himself a wartime pilot, an emergency-room surgeon, and a devil-may-care killer. The character's name has come into more general use to refer to an ineffectual dreamer, appearing in several dictionaries.The American Heritage Dictionary defines a Walter Mitty as "an ordinary, often ineffectual person who indulges in fantastic daydreams of personal triumphs". The most famous of Thurber's inept male protagonists, the character is considered "the archetype for dreamy, hapless, Thurber Man".

Although the story has humorous elements, there is a darker and more significant message underlying the text, leading to a more tragic interpretation of the Mitty character. Even in his heroic daydreams, Mitty does not triumph, several fantasies being interrupted before the final one sees Mitty dying bravely in front of a firing squad. In the brief snatches of reality that punctuate Mitty's fantasies the audience meets well-meaning but insensitive strangers who inadvertently rob Mitty of some of his remaining dignity.