Yandere (ヤンデレ) is a Japanese term for a person who is initially very loving and gentle to someone (or at least innocent) before their devotion becomes destructive in nature, often through violence and/or brutality.

A yandere is a person (usually female) who is obsessed with someone to the point that they are will to do anything to be with that person. This can include(not limited to) killing people, threatening people, harming people, (etc.). Now although usually seen in only animes, there are some real cases of yanderes in the real world.

A character, usually a girl, who fits the archetype of being genuinely kind, loving, or gentle, as well as obsessed with their love interest, sometimes demonstrating this through violent behaviour often killing those who try to harm,take or talk to their love interest.

Source : wiktpedia (yes it's spelled that was)

A yandere is a person either in anime or real life who would harm or kill others for the one they love. In anime they usually love the mc (main character).

Seems kind and gentle in the outside, but actually very brutal.

Yandere is an anime/manga slang for a character who is caring and loving at first, but who gets more psychotic and delusional in the end. Yandere character also usually shows obsessive and brutal traits.

Yandere is a compination of words yanderu (to be sick) and derere (exhausted or love sick).

Yandere is somewhat similar to terms tsundere and kuudere as these all describe characters attitude and how the character matures during the show.

When a person kills or hurts a person because they like the yandere's crush