Sin is the negation of the commands of God.You have sinned towards God and also towards humans whenever a law or code of ethics is broken .
There are however 3 different philosophys of sin.
1) The first and original sin is the sin of Adam and Eve,This is the sin of disobeying Gods command not to eat the fruit of knowledge.All Jews ,Christians and Muslims belief in this sin but they differ in that the Christians belief that the original sin is inherited by all humans and that all humans can only be forgiven by God only though or by praying to Jesus, because Jesus is according to them,the son of God.Jews ,Muslims,Hindus and other religions offcourse do not belief in such kind of philosophy of sin.
With this philosophy of sin the Christians managed to have monopoly over Gods fogiveness and Heaven.Whether this philosopy is true or false is irrelevant, but it certainly is a clever way of playing a game of monopoly and and politics.
2) The second philosophy of sin as beliefed by Muslims and othe religions is that a child is born sinless and the only sin when they have grown to recognise the ethics and law of God from the people who teach them.
This kind of philosophy is easier to understand and is without strings attached. The rational of Jesus having to carry other peoples sin is not very logical.
This philosophy of sin therefore turns upside down the the Christians philosophy.
3) The third philosophy of sin is one that is undestood and beliefed by the Sufi Muslims
This philosophy of sin is based on the unity of God. God is the creator of all things. He created the angels and also created the satans.
This makes Him the originator of good and bad. Verses of the Quran point to the fact that it is He who guides whoever he wishes and it is He too who misguides whomever he wishes.
This makes us humans very like robots, or as stated in the Quran ..a slave of God..without a will power of his own. Thus having lost their ability to sin,they do not think of heaven or hell.They only ask for God.