Satanism is the practice of worshipping Satan. That is the core meaning, and it is the one to learn first. Though actually, people use the word in more than one way, and that is where talk gets messy. Some groups really do centre their religion on Satan. Some other groups take the name but say they do not believe in a real Devil; they are using the name to push against church rules. Newspapers and films often throw satanism at anything they find dark, shocking, or “too heavy-metal,” which is looser than a careful meaning. In everyday English the word feels serious and often scary; it is not a casual joke word, even when people use it carelessly.