A label applied by many about another person, specifically about that persons morals. This label when applied to anyone is then often used to pursue ones personal goals by punishing the
individual labeled as evil, most prominently by spreading wide and far that the person is evil. There are many ways to apply this label, and it is 99 percent of the time mislabeled, due to the clause that whomever wins, regardless of who they are, writes history. It doesn't take a genius to see
the problem there.
In reality, evil is simply defined as an act most prominently marked with only
personal gain, and not gain of the society.