According to common usage today, heresy is false belief or false teaching. It is the misguided opinion of someone who denies the orthodox teaching of the Bible.
However, the word is used in this sense only once in the New Testament. Elsewhere it means sect or party. The Sadducees and Pharisees were sects within Judaism (Acts 5:17; Acts 15:5). Orthodox Jews considered the Christians a Jewish sect who followed Jesus the Nazarene (Acts 24:5; Acts 24:14; Acts 28:22).
When used by Christians, the word referred to factions created within a church through lack of love towards others (1 Corinthians 11:19). Those who created such factions showed that they were directed by the flesh, not by the Spirit (Galatians 5:20). Such people were to be warned, then avoided, if they did not cease their divisive practices (Titus 3:10).
Because false teachers created factions, the word ‘heresy’ developed its more familiar meaning of ‘false teaching’. The one biblical reference to heretics in this sense is to false prophets who deny Christ. By their belief they destroy themselves and by their teaching they destroy others (2 Peter 2:1; cf. 1 John 2:22; 1 John 2:26; 1 John 4:1-3).