Heresy is a term used in Christianity to refer to any belief or practice that goes against the official position of the church. The word "heresy" comes from a Greek word meaning a self-chosen opinion or the sect holding that opinion. In the New Testament, the word "heresy" is used to denote a sect or division that threatened the unity of Christians. Heresies are self-chosen doctrines that do not originate from God and explicitly undermine the gospel. According to the Apostle Paul, a heresy is false doctrine that is damnable, any belief that leads to anathema, condemnation to hell.

Heresy has existed in every age, but during the 12th century, the Catholic Church took unprecedented action against it. The church increased the severity of punishment for heresy, ultimately making it a capital offense. The churchs power to judge extends only to warning and expelling sinners from the church when they refuse to repent.

In summary, heresy is a belief or practice that goes against the official position of the church and explicitly undermines the gospel. It is a self-chosen doctrine that does not originate from God and can lead to anathema, condemnation to hell. The church has been careful about using the label heresy, restricting it to beliefs that clearly undermine the biblical gospel.