"A Heretic does not believe exactly what I believe and is therefore an abomination."
Above is an intolerant viewpoint. Many different Religions 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.