I love philosophy, so I am delighted to give my opinion on this matter. This I will do in two parts, the first of which will handle the original question itself.
From the beginning of recorded history and probably beyond we have asked the question of the nature of good and evil. The answers are as diverse as the people who asked. Lets try it, too.
If you think about it, you will realize that there is no “good” or “evil” in an absolute sense – those terms are inherently relative . You cannot even define one without the other, for they are merely opposite degrees of the same thing, just like hot and cold (actually this is true for pretty much everything, as the German philosopher Hegel knew). How to know the good without knowing the bad? 
But that is not where the relativity ends. Generally speaking, the acts we perceive as “evil” are those that are done on purpose and are bad for someone. However, what is bad for one might be good for another. For example I might go for and get the job you needed so desperately. Moreover, this is not limited to one species either. If a virus spreads globally, that is a plague for humanity, but a blessing for the virus.
The great Sadhguru of India says whether an action is good or evil is judged by four things:
- the intention behind it
- what consequences it generates
- how those consequences affect the judge
- how the judge sees the world
So ultimately, everyone decides that for themselves based upon their own knowledge, set of values and beliefs. Together, the sum of those individual decisions form the collective morality of a culture. But Morality keeps changing. From society to society, from generation to generation, from human to human it is different. 
As a consequence, we need to find universal values that transcend culture, time and even species to decide on what is “good” and what is “bad” or “evil”. We will not be able to define absolute goodness, that remains impossible. What can be done is assuming the highest and most inclusive perspective to look at the subject matter, though. This is what we will attempt in Part II.
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 Will Durant: The Story of Philosophy, the Lives and Opinions of the Greater Philosophers, 1926
 https://www.youtube.com/watch?v=FJcHN6wzViA, as of 2020-03-30
 Dalai Lama: Ehics for the new Millenium, 1999