From the perspective of a crow, Nihilism is thus:
The realization that just about every viewpoint a human has, about the way things are, is completely arbitrary, and hence suspicious.
Society, and its rules, are arbitrary. They have no basis in reality.
Civilization, itself, is arbitrary. It is a group of people agreeing to behave in certain ways, so that they are all on the same page.
Not much of this social interaction is truth. It is almost all made-up, by crazies who like their own ways of seeing life, as opposed to understanding what life actually is.
Therefore, Nihilism is a good starting point to discover the truth of things, and a baseline from which to sortie outwards in the exploration of - and search for - reality.
On the other hand, Nihilism is not:
Behaving like a devil-worshipping, disgusting, scurrilous cannibal, in order to show others what a brilliant and irreverent rebel one is.
This is not a widely-held, or popular definition of what Nihilism is, but rather what a crow makes of it, from the limited exposure a crow has, to such things.
Do feel free to correct or modify this description, to explain your own ideas on Nihilism.