Outside of a religion, the concept of “sin” is meaningless. Since there are diverse religions on earth, there are diverse understanding of what constitutes sin. Essentially, they can be taken as a “particular wrong” in a particular religion.
In the “Abrahimic religions” of Judaism, Christianity and Islam, the ideas of sin varies.
Judaism regards the violation of the divine commandments to be a sin. Judaism teaches that sin is an act, and not a state of being. Humankind was not created with an inclination to do evil, but has that inclination "from his youth"(Genesis 8:21). People do have the ability to master this inclination (Genesis 4:7) and choose good over evil (conscience)(Psalm 37:27). Judaism uses the term "sin" to include violations of Jewish law that are not necessarily a lapse in morality. The generic Hebrew word for any kind of sin is avera (literally: transgression). Based on verses in the Hebrew Bible, Judaism describes three levels of sin. There are three categories of a person who commits an avera. The first one is someone who does an avera intentionally, or "B'mezid." This is the most serious category. The second is one who did an avera by accident. This is called "B'shogeg," and while the person is still responsible for their action it is considered less serious. The third category is someone who is a "Tinok Shenishba", which is a person who was raised in an environment that was assimilated or non-Jewish, and is not aware of the proper Jewish laws, or halacha. This person is not held accountable for his or her actions.
In Christianity, there is some difference in the understanding of sin between the Roman Catholics and the Protestants. Roman Catholic doctrine distinguishes between personal sin and original sin. Personal sins are either mortal or venial.
Mortal sins are sins of grave (serious) matter, where the sinner is fully aware that the act (or omission) is both a sin and a grave matter, and performs the act (or omission) with deliberately and consciously. The act of committing a mortal sin cuts off the sinner from God's grace; it is in itself a rejection of God. If left un-reconciled, mortal sins result in eternal punishment in Hell.
Venial sins are sins which do not meet the conditions for mortal sins. The act of committing a venial sin does not cut off the sinner from God's grace, as the sinner has not rejected God. However, venial sins do injure the relationship between the sinner and God, and as such, must be reconciled to God, either through the sacrament of reconciliation or receiving the Eucharist.
Original sin -- Most denominations of Christianity interpret the Garden of Eden account in Genesis in terms of the fall of man. Adam and Eve's disobedience was the first sin man ever committed, and their original sin (or the effects of the sin) is passed on to their descendants (or has become a part of their environment).
Many Protestants teach that, due to original sin, humanity has lost any and all capacity to move towards reconciliation with God (Romans 3:23;6:23; Ephesians 2:1-3); in fact, this inborn sin turns humans away from God and towards themselves and their own desires (Isaiah 53:6a). Thus, humans may be brought back into a relationship with God only by way of God's rescuing the sinner from his/her hopeless condition (Galatians 5:17-21; Ephesians 2:4-10) through Jesus's ransom sacrifice (Romans 5:6-8; Colossians 2:13-15). Salvation is sola fide (by faith alone); sola gratia (by grace alone); and is begun and completed by God alone through Jesus (Ephesians 2:8,9).
This is in contrast to the Catholic teaching that while sin has tarnished the original goodness of humanity prior to the Fall, it has not entirely extinguished that goodness, or at least the potential for goodness, allowing humans to reach towards God to share in the Redemption which Jesus Christ won for them. Some non-Catholic or Orthodox groups hold similar views.
Buddhism does not recognize the idea behind sin because in Buddhism, instead, there is a "Cause-Effect Theory", known as Karma, or action. In general, Buddhism illustrates intentions as the cause of Karma, either good, bad, or neutral. Furthermore, most thoughts in any being's mind can be negative.
Vipaka, the result of your Karma, may create low quality living, hardships, destruction and all means of disharmony in life and it may also create healthy living, easiness, and harmony in life. Good deeds produce good results while bad deeds produce bad results. Karma and Vipaka are your own action and result.
Pañcasīla (Pāli) is the fundamental code of Buddhist ethics, willingly undertaken by lay followers of Gautama Buddha. It is a basic understanding of the Noble Eightfold Path, which is a Buddhist teaching on ways to stop suffering.
In Hinduism, the term sin (pāpa in Sanskrit) is often used to describe actions that create negative karma by violating moral and ethical codes this differs from other religions like Judaism, Christianity and Islam in the sense that sin is against the will of God. In fact, it is often described in the scriptures that chanting the name of Hari or Narayana or Shiva is the one of the ways to atone for sins, prevent rebirth and attain moksha.
(Of course, the above views stand to be corrected.)
NEXT: The idea of Sin: -Part 3: Islam.