There is no such thing.
Humans believe anyone who does anything immoral or unethical, anything deliberately harmful physically or mentally, (including emotionally) is sinful.
But humans are a passing phase on the way to extinction as they come into their true spiritual status.
Mystics achieve a status of very high consciousness of existence through the actual personal experience of the Mystical Experience of the Reality (MER), in which we all exist whether we like it or not. They have responded by submitting, submerging themselves to Reality.
Unlike many ideologies such as religions, coercion is no part of this call (which is in all of us whether we listen or not. Your turn will come, in Reality’s own good time).
This absorbtion into Reality is irrisistible, welcomed with joy and humility. Mystics can be believed – there is no such thing as sin in their mystic experience.
So Sin is only a human word, limited to the human race. It has no meaning or even existence in MER.
Yes, the word sin exists in all religions but probably lost its proper, more loving MER meaning – to ignore one’s calling to Reality – after the religions’ mystic founders died.
Was sin – and is it still – a disciplinary device to promulgate each religions’ interpretation of how humanity must collectively reach its destiny by us all doing as we’re told while we’re here, in faith, belief and hope, i.e. by “faking it until we make it”, rituals, symbols, songs, dresses and funny hats, wound head gear, beards, covered faces, subduction of species and so on, and so on – manmukh!, manmade stuff?).
The bottom line of being human is simple: you are your only access to MER.
Religion and society and their artificalities are no excuse to ignore your true, individual, custom made destiny awaiting you in Reality.
As for Society, that greatest of sins against MER, it must serve your needs, not the other way round. You are not an ideological commodity.
Mystical Experiences of Reality 
Sin is not defined by human beings, because sin is defined as a crime committed against God and His Law. The word sin is a religious term, not simply a human word, and cannot be understood outside a religious context — whether it is Judaism, Islam, or Christianity.
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