Tsundere

Tsundere (ツンデレ) is a Japanese word for a character archetype which describes a person with a conceited, spiky, combative 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 personality that is good-willed, but its attitude and actions often contradict its nature. 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.

Tsundere is an Internet slang word that has a remarkable subdivision structure; usage rules vary accordingly. Therefore, the term is not elaborately defined as to what character types can be described as tsundere; the term transcends gender and species. The definition is often subjected to the creator's point of view.

Tsundere is a combination of the two words tsuntsun (ツンツン), and deredere (デレデレ). Tsuntsun is defined as "aloof, morose, pointed", and deredere is defined as "exhausted, lovestruck". Tsunderekko (ツンデレっ娘) is a related noun, referring to a girl with a tsundere personality. Like nekomimi, tsundere is considered a moe-inspiring character trait.

INFO taken from wikipedia