Lunfardo (Spanish pronunciation: [luɱˈfaɾðo]; from the Italian lombardo or inhabitant of Lombardy in the local dialect) is an argot originated and developed in the late 19th and early 20th centuries in the lower classes in Buenos Aires and from there spread to other urban areas nearby, such as the Greater Buenos Aires, Rosario and Montevideo.

Originally, Lunfardo was a slang used by criminals and soon by other people of the lower and lower-middle classes. Later, many of its words and phrases were introduced in the vernacular and disseminated in the Spanish of Argentina, and Uruguay. Nevertheless, since the early 20th century, Lunfardo has spread among all social strata and classes by habitual use or because it was common in the lyrics of tango.

Today, the meaning of the term lunfardo has been extended to designate any slang or jargon used in Buenos Aires.