NIHILISM THE DOCTRINE THAT THERE IS NO MORAL PURPOSE IN LIFE AND MORALITY IS NOT REAL
Nihilism says that there is no moral right or wrong. And if there is no moral right or wrong there is no neutral either.
Nihilism argues that right and wrong have no meaning and it is assumed that that means you are absolving yourself of trying to make a difference. Nothing matters. You can offend and hurt people and tell yourself that their false perception that respect matters is to blame. Since others do not matter the only relationship you have will be with yourself. Nihilism reportedly tells people not to waste their time on God or love or happiness for they only seem to be important and are in fact not. Now despite all that, nihilists actually tend to approach things this way, "I may as well take action. I may as well not go out of my way to offend. I will not tell people to waste their time on God or love happiness for atheism or hate/indifference or unhappiness is a waste of time too." Most nihilists are just like everybody else. And there many of them lurking in Christianity and Islam.
Nihilism tends to be cherry-picked by those who would not identify as nihilists. There is the Christian doctrine that sin such as murder or adultery or kidnapping does not matter if you want to be saved and enjoy eternal life. What matters is the failure to repent of them and to receive God's pardon and healing. So if they do not matter then repenting cannot matter either. And a God who condemns the sins but does not really care is hardly a God you can trust to live with forever. A God who demands repentance from sin not because of the sin is insane. Scores of examples of overlaps with nihilism exist. You would need every page on earth to record them on.
Ethical Nihilism does not say all is permitted. If it did then it be saying it is morally right to do what you want. That is not denying morality but replacing it with a permissive version. Equating Nihilism with All is Permitted is a popular mistake.
There is Practical Nihilism and Ethical Nihilism. Practical Nihilism as opposed to Ethical Nihilism does not necessarily deny that we might be able to work out what right and wrong are but might tell us to assume there is none when we don't know. Religion is the major cause of that kind of Nihilism.
You can talk about Passive Nihilism and Active Nihilism. The passive just thinks there is no point in acting. The active acts but sees no point.
The iconoclast can say that all is permitted and permission doesn't matter anyway for there is no God there to permit. One will be unable to be consistent with this. But if all is permitted then you are permitted to say adultery is immoral. You may even say that inconsistency is fine for all is permitted.
Ethical Nihilism can be sectioned off so you can be Nihilist with the unborn in terms of abortion and not other things. You can say that the unborn child at any stage is worthless and can be brought out of the womb to be tormented but you can still battle hard against animal testing.
You never really know if somebody is or is not an Nihilist or in what they are Nihilist. They may not realise it themselves.
A Nihilist who tries to commit to Nihilism and is not very successful is still a Nihilist for a label is earned by trying. If you don't try the label does not describe you.
Is nihilism a feeling not a philosophy?
The first thought is that for some it might be. It can be both.
Those who say they do not desire the good are contradicting themselves for desire always seeks some good. They desire to be seen as not desiring the good which is a different thing.
People make a difference between desiring what is good and desiring immediate satisfaction. But desiring the good can be a form of immediate satisfaction. If you can use alcohol with all its troubles for immediate satisfaction then why can't you treat love and justice in that way? If we are about the fast rush, the thrill we can reach and get, then none of us are far from being like the nihilist.
