Heresy

Heresy is a belief system which disagrees with the, ”One True Faith”, what ever that is. There are as many different versions of the True Faith as there are different believers though some oppressive Religions and Religious cults try to impose the beliefs of the leaders onto all members.

Heretic
"A Heretic does not believe exactly what orthodoxy requires and is therefore an abomination." Above is an intolerant viewpoint. Many different Religion]] and Sects are intolerant. Other religions and sects are more tolerant and tend not to use words like heretic. Typically a heretic disagrees with the “True Believers” in some ways but still belongs to the religion. Those disagree radically and don't belong to the religion are seen as unbelievers or infidels.

Tolerance and intolerance
Some religions and some individuals are tolerant of those who disagree with them. Others are thoroughly intolerant. Historically Roman Catholics and Protestants have been imaginative in finding ways of torturing and killing those  they saw as heretics as have Islammic fundamentalists.