Tsundere is a character archetype which describes a person with a conceited, irritable, and/or violent personality that suddenly becomes modest and loving when triggered by some sort of cause (such as being alone with someone). It can also describe a contradictory personality which is good-willed on the inside, but with a harsh attitude on the outside. Originally found in Japanese bishōjo games, the word is now part of the otaku moe phenomenon, reaching into other media such as anime, manga, novels, and even mass media.
For the example of TSUNDERE Character:
Shana( Shakugan no Shana)
TSUNDERE!!
Aisaka Taiga (Toradora!)
Louise (Zero no Tsukaima)
Sanzenin Nagi ( Hayate no Gotoku)
Kannagi Ayano ( Kaze no Stigma)