From the Wikipedia...
A
sausage consists of ground meat and other animal parts, herbs and spices, and possibly other ingredients, generally packed in a casing (traditionally the intestines of the animal), and preserved in some way. Traditionally, sausage casings were made of the intestines of animals. Today, however, natural casings are often replaced by collagen, cellulose or even plastic casings, especially in the case of industrially manufactured sausages. The word sausage is derived from Old French
saussiche, from the Latin word
salsus, meaning
salted. Wieners, salami and Weisswurst are examples of sausages from different classifications. More info
here.
A
hot dog is classified as a type of
sausage or, alternatively, a sandwich on a suitably shaped bun with the sausage and condiments on it. Also called a
frankfurter (named after the city of Frankfurt am Main, Germany) or a
frank and a
wiener (named after the city of Wien, Austria known as Vienna in English).
Hot dogs were frequently known as
frankfurters or
franks until
World War I, when the name was changed due to anti-German sentiment (see freedom fries). After the war the original name returned to common usage. More info
here.