What is a derringer?

Remington type derringer
   The derringer is a small pocket pistol. This handgun was designed and manufactured by the famous gunsmith Henry Deringer. He and his father established an armory in Philadelphia in 1806 and made all types of flintlock and percussion-cap firearms. The finely designed pocket-size percussion-cap pistol, manufactured at the armory between the 1840's and the Civil War, was the most celebrated of Deringer's weapons. These small pistols were the standard weapons used by gamblers in the pre-Civil War period. John Wilkes Booth used a derringer to shoot President Abraham Lincoln. Henry Deringer died in 1868, and his armory went out of existence soon afterward.