Sin is transgression against the Law of God. The identification of sin on the other-hand is what has people confused. For the most part sin falls into 3 categories, sin against God, sin against others and sin against self.
Jesus ushered in the Law of love. His love is unconditional and forgiving. I am persuaded that you cannot walk in His love unless you are born-again and filled with the Holy Spirit. Being born-again gives you understanding and compassion for others and being filled with the Holy Spirit gives you power to demonstrate that love and to walk in forgiveness.
Romans 13:10 Love worketh no ill to his neighbor, therefore love is the fulfilling of the Law... Sin, is anything that "works ill" to another.