For many of you, the answer is clear: Chianti is a winegrowing region within Tuscany, Italy. However, for those who have drunk Chianti before — perhaps many times — yet never really knew what it meant, you can learn all about it by following this link: Chianti Wine Basics.
That page will cover the very basics of wine from the Chianti region. If you want a really detailed explanation or reference, consider purchasing this book from Amazon: Chianti and the Wines of Tuscany