Belarusian languageBelarusian, or "Byelorussian", spoken in and around Belarus, is one of the three East Slavic languages. It is also written "Belarusan", "Belorussian". The adjectives "Belarusian" and the like were coined in the 1990s by some English-speaking people to denote something or somebody of or pertaining to present-day name of Belarus, its people and the language they speak, whereas in Russian and Byelorussian no new forms of the adjective appeared in those days. As a result, both "Belarusian" and well-known "Byelorussian" are used. Some people would strongly recommend to use "Balarusian" with the nouns that pertain to the state and people of Belarus, not language.
The Belarusian language has evolved considerably from its early roots, as the dialects of Ruthenian (East Slavic Orthodox) spoken in the territory of the Grand Duchy of Lithuania. A standardized version of Ruthenian became the official language of the Grand Duchy of Lithuania. By the 16th century, the term "Ruthenian" referred to the language spoken in modern-day Ukraine and Belarus; a process of divergence that accelerated in the 17th century created a new division between the languages spoken in the south (Ukraine) and north (Belarus) of Ruthenian-speaking territory.
Like Ukraine, Belarus and the Belarusian language has been subject to heavy Russification. Unlike Ukraine, Belarus has historically lacked a strongly nationalistic population, which tends to identify itself as a close associate of Russia (if not Russian outright). This lack of a strong ethnolinguistic identity, along with the popular association of Belarusian dialects as rural peasant languages as opposed to Russian's modern/urban connotations, is seen by some to threaten the eventual extinction of the Belarusian language in Belarus. The Russophile foreign policy orientation of Aleksandr Lukashenko's government in Belarus is seen as further threatening the Belarusian language.
Addition: The Belarusian language is written not only in the Cyrillic alphabet (with several unique letters), but also in Lacinka (Latin script) and Arabica (Arabic script). Nowadays, the Arabic script is no longer used, but many people continue to write in Lacinka, although officially only the Cyrillic script is supported. More articles here.