Anyone who engages in actions, statements, or thoughts against the Imperial Truth of the God-Emperor of Mankind.

Such categories for groups that would be classified as Heretics include, but are not limited to: Furries, SJWs, anime girls, communists, anarchists, Nazis, environmentalists, etc.

A siphoner witch who is also a vampire

A broad term usually applied to: Orks, furries, feminists, college students, Tumblr users, Reptilians, and ten year olds.

According to the Heresy Decree by the Law of the Imperial Truth, any members within these groups is automatically deemed a heretic.

A broad term usually applied to the lowest forms of humanity out there: Orks, furries, feminists, college students, Tumblr users, Reptilians, and anime goddesses.

According to the Heresy Decree by the Law of the Imperial Truth, any members within these groups is automatically deemed a heretic.
According to the Codex Astartes, "All Heretics are to be purged instantly. If non-Heretics are found sheltering, befriending, or in any way expressing sympathy to a Heretic, they are, themselves, Heretics, and are to be purged at once."

That one gay kid in your class

Is the most badass mutha fucka from Hell!!
MUHAHAHAHAHAHHA!!!!

A trator: one who rebels against ones nation.

Also a game on Halo2