Matatabi is the two tailed bijuu in the anime Naruto Shippuden. Matatabi is introduced in the 313 manga chapter and episode 72 of Naruto Shipuden. Matatabi is more commonly known as the Two-Tails.
The tailed beasts in Naruto are commonly known as Bijuu. The Bijuu are also referred to as "Chakra Monsters", since they are living forms of chakra. The tailed beasts have a history of their own and here it is.