The word "derringer" was a generic name for super-compact pistols of the 19th Century. The title stemmed from the surname of the father and son gunsmith team made up of Henry Deringer, Senior and Henry Deringer, Junior. The pair plied their trade out of Philadelphia, Pennsylvania from the early part of the century into the late 1860s. Despite their name becoming associated with the handy, concealed-carry pistol, their trade also involved rifles and dueling pistols though it is their pocket designs that were openly copied throughout the industrialized world. For reasons lost to history, the name of the weapon "derringer" adopted a second "R" unlike the actual "Deringer" family name. Henry Deringer, Jr survived until 1868 to the age of 81 by which time the family business had suffered enough to close down forever. No patent was ever filed for the derringer designs which proved popular with the masses.
Generally, derringer pistols were large-caliber weapons utilizing very compact frames. They were often of single-shot or even twin-shot configurations actuated by a trigger pull and a flintlock or percussion cap arrangement (the latter seen in later models). Due to their compact size, they were perfect guns for concealment in a coat pocket, or a lady's purse, and useful in extremely close-range confrontations. Deringer produced their small pistols in matching pairs typically delivered in ornate showpiece boxes (consistent with pistols of the period). Each design varied in caliber and barrel length.
Derringer pistols have proven equally popular in Hollywood Westerns where the gambler or hero usually carries one, or a pair, in a spring-loaded contraption hidden under the sleeve or simply in a leg boot though it is reasoned that their use in real life was far more conventional.
According to sources, derringers were used to a certain extent in the American Civil War despite their not being true "military-minded" weapons.