From Wiki:

In Western philosophy, evil is usually limited to doing harm or damage to an object or creature. Plato argued that which we call evil is merely ignorance and that good is that which everyone desires. Benedict de Spinoza said that the difference between good and evil is merely one of personal inclinations: "So everyone, by the highest right of Nature, judges what is good and what is evil, considers his own advantage according to his own temperament... ."[2]

The duality of 'good versus evil' is expressed, in some form or another, by many cultures. Those who believe in the duality theory of evil believe that evil cannot exist without good, nor good without evil, as they are both objective states and opposite ends of the same scale.

The legal term, malice (from the Latin malus meaning "bad") describes the deliberate human intent to harm, while sadism refers to a psychological state in which a person derives pleasure from the pain of another person.

In the philosophical concept of evil, the intent to cause harm is crucial, so that acts that would otherwise be considered evil are not called evil when performed by very young children, by animals, or by the insane (see Amorality).

There is also a class of deliberate acts, known to be harmful to another, which are not considered evil because:

1. they are acts of self-defense or defense of another
2. they are considered justified (for instance, Just War)

Phew. The debate about what constitutes evil has kept many philosophers busy for their entire life times. As such, I think it falls outside the scope of the current discussion.
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Extraordinary claims require extraordinary evidence - Carl Sagan