Original sin (read more) is a concept, about Adam and Eve's fall from Grace, and eviction from the Garden of Eden. As detailed in the Old Testament.
It is not a phrase used in the Bible.
In fact, some Jewish groups rather resent it; seeing it as an imposition of a Christian theological view upon what was, after all, events in a sacred Jewish text. St. Augustine, alive 354-430 AD is the thinker credited with the Original Sin idea. Augustine lived long after Jesus was around, and the New Testament (Christian Bible) itself was written.
The Doctrine of Original Sin is not accepted by all Christian denominations; not in the Eastern Orthodox Churches, for instance. In contrast, other sects not only accept all of Augustine's ideas, but see them as leading logically to the concept of predestination (God knows since before you were born if you will be saved).
The doctrine of the Original Sin has its basis in the Bible. It is the condition or state of sin into which each human being is born due to the sin of the first man, Adam, who disobeyed God in eating the forbidden fruit (of knowledge of good and evil) and, in consequence, transmitted his sin and guilt by heredity to his descendants.
This condition of the human nature is accounted for by the story of the Fall of Adam in the book of Genesis. In the Gospels there are no more than allusions to the notion of the Fall of Man and universal sin. The main scriptural affirmation of the doctrine is found in the writings of Paul and particularly in Romans 5:12-19, in which Paul establishes a parallelism between Adam and Christ, stating that whereas sin and death entered the world through Adam, grace and eternal life have come in greater abundance through Christ.
Theologians divide sin into "actual" and "original." Actual sin is sin in the ordinary sense of the word and consists of evil acts, whether of thought, word, or deed.
As I understand it, while the term 'Original Sin' is not to be found anywhere in the Bible, the concept IS in fact solely based on what Paul says in 'Corinthians 1, 15:22', where he (Paul, not Jesus(a.s)) says, “For as in Adam all die, even so in Christ shall all be made alive.” He then uses that as a building block to explain the theory in the the Fifth chapter of his letter to the Romans, and that is where Christianity derives it from. St. Augustine, alive 354-430 AD is the thinker credited with the Original Sin idea. Now, adherents of Judaism, the Jews believe in the Old Testament, which essentially comprises of Moses'(a.s) Pentateuch amongst other books, however they (the Jews) deny the concept of the original sin based on what 'their' own scriptures say; but it must be noted that they do NOT deny the story of Adam(a.s), and how he and his wife were tricked by the 'serpent' into eating of the tree and thus earning the subsequent wrath of Almighty God leading to their banishment from the Garden. Islam, the 2nd largest of the Abrahamic faiths is (out of all the others) the ONLY one which makes it an article of faith for its adherents to believe in Adam, Jesus, Moses, Cain, Able, Jonah, Noah, Abraham, Ishmael, Isaac, Lot, and all other individual links in the large chain of messengers (peace be upon all of them) sent by God Almighty for guiding mankind unto the 'straight path'. We Muslims are thus commanded to believe in the story of Adam and his wife in the Garden, and its aftermath (with some differences of opinion course), in addition to the fact that there does exist some amount of truth in the existing Jewish and Christian scriptures, while other parts of it have been corrupted over time. It is this belief that gives rise to the dispute on the concept of Original Sin (which, I repeat is not mentioned by word in the Bible except as a conceptual reference by Paul). Islam is closer to the beliefs of Judaism and Christianity than ANY other major religion in the world. Thus, owing to the facts that a) Islam teaches about Adam and Eve, but denies the Original Sin concept completely, and b) Asks Muslims to believe that books were revealed to messengers like Moses(a.s) & Jesus(a.s) before the Qur'an was revealed to Muhammed(pbuh) however they were corrupted over time (giving rise to disputes like the one in question, I might add), would make it essential that whenever there be mention of a topic common to all three religions, all viewpoints be mentioned adequately and accurately
To add to the above answer, about the only thing left out, the doctrine of original sin states that, since Adam first brought sin into the world, all human beings are born with a sinful nature and, without the salvation of Jesus, cannot be redeemed. The exception is, of course, the one perfect human being, Jesus himself.
Many people find it hard to accept that small babies are not born innocent because they fear it means that an infant that dies before the age of responsibility must be doomed to be lost. Most of us who accept the doctrine of original sin also believe that Jesu's salvation covers all who are too young or too disabled to actively choose between right and wrong.