The native language in
Belarus, or
White Russia. The language is closely related to
Russian, and in fact is one of three languages that trace their roots to
Old Russian, the other two being
Russian and
Ukrainian. The three languages diverged mainly after the
Mongol conquest of
Kiev Russia.
Belorussian was heavily influenced by both Polish and Lithuanian, but is still very close to Russian. The language dropped some of the more esoteric cases of the Russian language, and the phonetics haved morphed closer to Polish.
There are about 10 million Belorussian speakers worldwide. They are mostly concentrated in Belarus, with significant minorities in Russia, Poland, and Ukraine.