The act of taking yourselves live.
It can have many reasons why people would commit suicide, and to make it easier i will split this up in 2 main cathgories.
1) Taking your live because you really want to.
2) Taking your live because you want to prove something.
Now the person who tries to take his own live because he wants to doesnt care about other people. He doesnt warn anyone, he doesnt show it to anyone and quite often doesnt even leave a goodbye message. This person will take her own live and you will not even notice that the person wants to until she does it.
There is no way to help this person as you will not notice before the suicide, and even if you stop the person whilst she attempts to commit suicide that wont help. This person will always look at suicide like the only way out and it will come back to her even 30 years after the first attempt.
The person who makes suicide because she wants to prove something doesnt really want to commit suicide. This person will gradually come into the phase and you will notice that if you are close enough. This kind of person needs help and she can be helped. Even if the person attempts to commit suicide she doesnt really mean it (the first time, maximum the second time) but if it comes to the point of attempting again then its most probably serious. Note that this person will need help all her live, and will always need someone strong at her side to help her all the time. Even if you might think this person is "cured" it can happen again that the person tries to commit suicide many years later.
Note to anyone who wants to attempt suicide:
Now many people say suicide is selfish but i wont go into that. The only thing i want to say is that if you do it, you obviously take your own live and noone elses so you should try not to harm people too much with it. Dont just jump under a car infront of a school and dont shoot yourself in the face because that just harms people close to you and people who love you. Even if you want to commit suicide, do you really want your mother to identify the corpse of your totaly splattered face? Do you want to give people a trauma that might stay all theyr live? If you want to commit suicide i know that i cant stop you so at least try to make it the less harmful for other then it can get.
"I decided that this live makes no sense anymore and that i cannot live with this pain, im sorry" - Commits suicide, noone ever suspected that the person would do that and they will always ask themselves why the person did.
Writes a text to the boyfriend "I think this is too much for me in my live, i am going to kill myself, i love you" - Boyfriend runs to girlfriend and stops her form doing it, then supports her on the way to the cure. This person didnt really want to die, but was so desperate that it was the only way to get someones attention on her problems.