A person (particularly female) who is romantically obsessed with an individual, most likely will use violent means to get the individual to love them and only them.

These individual’s suffer from low self-esteem and have Borderline Personality Disorder.

A Yandere is someone who comes obsessive to you when it comes to love. They might be sweet at first glance, but they will act violently towards the people you are connected to you.

The state or being a yandere.

The one reason to want a conservative family (granted, with guns) as your Neighbors.

Synonym for not dying alone.

A Yandere is a person who is willing to eliminate anyone who is interested in someone they love.
A Yandere is a combination of the words Yanderu(Mentally sick) and Deredere(Lovestruck)
It's common slang nostly used in anime and the game "Yandere Simulator".
They are usually and most commonly female.

They try to present themselves as cute and innocent and hide in plain sight.

Someone who is overall obsessed with anyone and does not hesitate to hurt someone just to be with the person they love.

Someone who kills for love. So, they basically have someone they love so much and they call them senpai~. If anyone goes near senpai~ they fucking kill them.