Persian is a language spoken in parts of the Middle East and Central Asia. It is also known by many people as Farsi, and less commonly as Dari or Tajik. Persian has over 60 million native speakers, with an additional 50 million speaking it in addition to their first language.
Persian is the official language of the nations of Iran, Afghanistan, and Tajikistan, and is spoken in parts of Iraq, Armenia, and Russia. While various dialects of Persian are in use throughout the world, they are all mutually intelligible, unlike some widespread languages such as Arabic and Mandarin. Differences in speech are not drastic between dialects such as Tajik and Dari, for example, though the alphabets used are entirely different.
The original alphabets of Persian -- one a derivative of the Aramaic alphabet, the other an Iranian script -- were phased out sometime in the 9th century in favor of the Arabic script. This came as a direct result of the region then known as Persia being converted to the religion of Islam, and the subsequent widespread use of Arabic in all religious, and many secular, writings. The Arabic alphabet used in Iran and other Persian-speaking parts of the Middle East is slightly altered from the standard Arabic alphabet, however, most notably with the addition of four new letters to add sounds not found in Arabic. Indeed, without one of these -- peh -- Persian would be unable to write the word Persian, instead having to rely on the Arabic spelling and pronunciation Farsi.
The Persian dialect of Tajik, the official language of the nation of Tajikistan, uses the Cyrillic alphabet, rather than the Arabic alphabet. This makes sense, given Tajikistan's close relationship with Russia -- indeed, many believe Tajik is a Russian-Persian dialect. In the parts of Afghanistan where Tajik is spoken, however, the Arabic alphabet is still used.
Persian is an ancient language, used in its modern form for more than 1100 years, and in ancient forms for far longer than that. In its past, it was spoken through a much greater swath of the world, and was even one of the major languages of India up until the time of the British conquest. The Hindi language was heavily influenced by Persian, and traces show up in a number of regional languages and dialects as well.
Persian has also contributed many words to English over the course of its history. These words include: bronze, caravan, caviar, chess, guitar, India, jasmine, khaki, lemon, lilac, magic, mummy, orange, pagoda, pajamas, paradise, peach, pistachio, rose, saffron, scimitar, sherry, sugar, tambourine, tapestry, and tiger. As the Greeks had substantial contact with Persia in early times, many English words come to us through the Latin, from the Greek, and originally from Persian.