My subjective definition:

Satanism is a religion that worships the devil. Satanists are evil, God-hating people, who, if they do not repent, will face Hellfire.

Objective definition:
In a more objective definition, Satanism is a religion which focuses on independence, self-preservation and vengeance. It focuses on aggression, ego and selfishness.

This is just a general definition that I have acquired from seeing the satanic rituals and processes performed by Satanists, actual Satanists and ex-Satanists.

My last words: Don’t turn to Satan, turn to God.

Satanism is ideological bullshit. There are two types of Satanism which are both equally bullshit:

Atheistic Satanism: Comprised of edgy atheists who ignorantly think their inherently selfish ideology is superior to all other ideologies. This form of Satanism teaches that one should worship themselves and give in to all carnal pleasures. LaVeyan Satanism is this type of Satanism which also teaches its adherents to believe in superstitious magic in the seventh rule of of its "11 Satanic Rules" that they teach.

The eighth rule declares that they shouldn't complain or cry over things "they needn't subject themselves to" like definitions such as this one. Yet like hypocrites, these atheist Satanists are constantly found on social media crying about Christianity which has no impact on their life and does more beneficial things for humanity than their ideology which in the 1st rule tells them not to preach their foolish opinions (like they do everywhere) "unless asked" and in the 11th, tells them to "destroy" anyone who bothers them.

All atheistic Satanists will also get triggered over people claiming they worship Satan despite the name of their cult originating from exactly that. Worship of the devil. Atheistic Satan Churches function similar to Scientology in that regular donations are required to ascend with ex-members being subjected to harassment and witch hunts by current members as LaVey's own daughter testified to when she left the Church of Satan.

The ultimate dogmatic justification for ego/power-trip-ful self-centered narcissism.

A group of pathetic emo nerds who feel enlightened yet still adhere to the ridiculous concept of religion by calling themselves satanists.

The religion of routing for gloomy disgusting wet weather; this religion is mostly confined to idiots with nothing better to do but wallow in misery with other Satanists; personal hygiene is not a pre-requisite for Satanists; most don’t believe in showers or any kind of fragrance and welcome members smelling like the stench of death.