Heresy

Heresy is to chose a different option—from hairein "to choose"—indeed, if a study of the world's oldest Office, the Romish "Catholic" Church is done, one finds it in heresy against itself.
Distinguished from Cursed Theory like Leninism. Heresy is only a sect, but a Cursed Theory is something that has historically has brought a great trouble.
Some heresies are e.g. dualist imitations of Christianity such as Marcionism.
Marcionism was an Early Christian dualist belief system that originated in the teachings of Marcion of Sinope at Rome around the year 144.
The Greek word was used by Church writers in reference to various sects, schools, etc. in the New Testament: the Sadducees, the Pharisees, and even the Christians, as sects of Judaism. Hence the meaning "unorthodox religious sect or doctrine" in the Latin word as used by Christian writers in Late Latin. But in English bibles it usually is translated sect. Transferred (non-religious) use in English is from late 14c.
"doctrine or opinion at variance with established standards" (or, as Johnson defines it, "an opinion of private men different from that of the catholick and orthodox church"), c. 1200, from Old French heresie, eresie "heresy," and by extension "sodomy, immorality" (12c.).