as it it used here,
comes from the Greek, meaning,
Disunion; division; sect.

Heresy came to mean, "A fundamental error in religion, or an error of opinion respecting some fundamental doctrine of religion." Since we now have so many different Christian churches, what is sound doctrine in one church may be 'heresy' in another; presumably a very good reason why God advised us against disunion, and different sects in the first place.

Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.
Galatians 5:19-21