Surzhyk (суржик, originally meaning "flour or bread made from mixed grains, e.g., wheat with rye, rye with oats etc") is currently the pidgin language most widely used in most of Ukraine. It is a mixture of Ukrainian substrate with Russian superstrate . Normally Russian vocabularly is combined with Ukrainian grammar and pronunciation.
The vocabulary usage of either of the languages varies greatly with location, or sometimes even from person to person, depending on the level of education, personal experiences, rural or urban setting, origin of his interlocutors. etc. The percentage of Russian words and phonetic influences tends to gradually increase in the east and south and around big Russian-speaking cities. It is commonly spoken in most of Ukraine's rural areas, with an exception of the westernmost regions, where the language does not contain elements of Russian, large metropolitan areas of Donetsk, Kharkiv, Luhansk, and especially Crimea, where virtually all of the population uses standard Russian.
Surzhyk is often used for comical effect. See, for example, the short plays by Les' Poderv'yans'ki.
There is a similar phenomenon in Belarus which is called trasianka.
See also