“Unbelievers” are those who do not believe in the God of the scriptures and are not rightly related to God through faith in his only son Jesus Christ. All men are born unbelievers and because of man’s radical and thoroughgoing depravity will remain in that state unless and until God sovereignly acts upon their heart and gives them the gift of faith, bringing them from darkness to light and eternal life. People who die in the state of unbelief will suffer just, eternal punishment.
“Heretic” is a word that has a somewhat flexible definition, but generally refers to someone who believes, or more specifically who teaches, doctrine that is a serious departure from “the faith once for all delivered to the saints.”