Sin
In Yahwism, sins are actions, thoughts, or behaviors that are forbidden by Yahweh. Since Yahwists consider Yahweh to be the supreme creator and arbitrator of all of reality, they believe sins to be objectively evil. In mainstream Yahwist religions, sin is usually considered to be inevitable, such that all humans (sometimes with the exception of particular prophets or holy figures) will sin at some point in their life; to make up for their sin, they must repent and beg Yahweh for forgiveness.
Many Christians believe that humans are born with the burden of "original sin," passed down from Adam and Eve when they committed the first sin by eating the fruit of knowledge in the Garden of Eden. This sin is not related to the actions of any individual human, but rather those of their forefathers. They believe that the only way to be redeemed of this sin, like all other sins, is to devote one's life to Jesus Christ, whom they view as the incarnation of Yahweh.
In Satano-Grigorism
Satano-Grigorism does not accept the existence of sin as an objective and universal property. Satano-Grigorists typically regard sin as synonymous to anything Yahweh does not approve of, and since Yahweh is a finite god like any other, his preferences hold no more objective authority than the personal views of any other being.
An action may be declared a sin by Yahweh for several different reasons, most of which can ultimately be traced to their likelihood to reduce people's dependence on, or loyalty to, Yahweh. One straightforward example is the prohibition of worshipping any gods other than Yahweh, because Yahweh is, by his own admission, a "jealous god." He seeks exclusive attention and submission from his worshippers and refuses to share an altar with other gods. Some sins, however, distract from him in less obvious ways. According to the Satano-Grigorist understanding, elevation of the Self and prioritization of the Self in a person's life makes them less likely to be dependent on and submit to Yahweh (or any other authoritarian being); this is the reason behind many of Yahweh's prohibitions. Some sins, such as lust and indulgence in the luxuries of life, are forbidden by Yahweh because enjoyment of the pleasures of the physical world encourages individual self-expression and independence, thereby elevating the Self.