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.