Fenya (феня) or fenka (фенка) is a Russian cant language used among criminals. Originally it was a cryptolanguage of ofenyas or ofenes, old Russian peddlers, and had a number of names. There are no convincing explanations about the origins of the words "ofenya" and "fenya". In modern Russian language it is also referred to as blatnoy language (Russian: блатной язык), where "blatnoy" is a slang expression for "criminal". It is also widely used in "thieves' songs".
The grammar is Russian; the vocabulary has changed over time.The original fenya consisted of broken Russian words borrowed from Greek and other foreign languages.