Kiswahili(language) as opposed to Swahili(people who speak Kiswahili) is a Bantu language, grouped with many languages from Central and Eastern Africa. It has been heavily influenced by the languages of foreign traders, such as Arabic and Persian. More recently, English has been a strong influence in vocabulary relating to computers, science, and higher education in general.
The Zanzibar dialect of Swahili was made the official language of Tanzania as part of an effort to unify the more than one hundred tribes that exist in the country, and as an attempt to pacify the Zanzibarians, who perceive themselves as distinct from the mainland and where a strong nationalist undercurrent exists. There are relatively few native speakers of Swahili (around 5-10 million), but a much greater number (over 50 million) speak it as a second language (their first being their own tribal language or dialect), owing to its use as the national language in several countries and as a lingua franca for most of East Africa (particularly Tanzania, Kenya, Uganda, Rwanda and Burundi).