Nihilism

1. An area of philosophy that posits that no social construct has true value and that human existence is inherently meaningless

It's useless to define it.

Contrary to popular definitions, Nihilism is not synonymous with cynicism or despair. Instead, Nihilism is a worldview in which one believes only in what one's observations and experiences seem to prove true, and that which can be otherwise proven true. That said, Nihilism varies according to the nature of the individual nihilist, but there are a few key ideas which are kept by nearly all of them:
1. The beginning of the universe was, within certain parameters, a basically random event, and the same holds for all events occuring since. It follows, then, that final purpose in things is false. Life, then, is an end-in-itself.
2. There exists no absolute truth regarding the value of any deed over another, such as right vs. wrong. Value systems, ethical codes, etc. are thus of no use to the Nihilist, except if they serve his best interests, increase their quality of life, or if they simply fall in line with what behavior would come naturally.
3. From the above it follows that responsibility, obligation, and the like are also falsehoods. Nihilists are thus inclined to ignore or sneer at societal norms and conditioned mentalities.
4. The first priority of every nihilist is his own well-being, satisfaction, and survival, and every action is ultimately done in the name of these things. However, he does not consciously pursue these ends; instead, he acts upon what feels natural and makes sense to him, and these naturally result. However, the above assumes that the Nihilist is in unity with himself, and possesses an undamaged psyche. In reality, some people are self-destructive by nature, and, if they took up a Nihilistic worldview, would seem to have a death-wish as the motive behind their actions. Since self-destructive individuals are common in modern society, this is probably how Nihilism has come to be seen as another word for despair.

A theory that life is without purpose, many things deconstruct to this after continuous questioning of why. From this, we realise value does not exist (without purpose it can't have extrinsic value)
Ethics and Morals become non existent and are merely thought to be invented by man for man to control man even though he has no reason to be controlled.

Also, Nihilists don't believe in anything. (Thoughts and ideas are not beliefs)

The belief in nothing.

Hey, the other definition is all well and but it missed the point. Nihilism is great! Nothing matters! Have a good time! Chill out! Be good to each other! Be a hippy/nihilist hybrid and love the world!

The absolute name invented to cover up one's inability to find meaning or self-worth. It's absolute character offers a pseudo-certainty in so far as it can never change. Thus by declaring myself to believe in nothing I have at last found an absolute to believe in and thus confer upon myself a permanent identity in the face of death. Nihlists like atheists are really somebody, unaware of the fact that he who believes in nothing actually believes in something.