Question: What is a heresy in the Bible?
Answer: The modern dictionary definition of a heresy is as follows:
Question: What is an example of heresy?
Answer: Arianism is one example of heresy.
What is Arianism heresy?
"Arianism is a Christological doctrine first attributed to Arius (c. AD 256–336), a Christian presbyter in Alexandria, Egypt. Arian theology holds that the Son of God is not co-eternal with God the Father and is distinct from the Father (therefore subordinate to him)." -Source: Wikipedia, Arianism
Question: Is there a biblical definition for heresy in the Bible?
Answer: For a clearer understanding into the definition of heresy, see this helpful quote from Bible Study Tools.
Heresy Bible definition:
"from a Greek word [αἵρεσις (hair-ee-sis),] signifying (1) a choice, (2) the opinion chosen, and (3) the sect holding the opinion. In the Acts of the Apostles ( 5:17 ; 15:5 ; Isaiah 24:5 Isaiah 24:14 ; 26:5 ) it denotes a sect, without reference to its character. Elsewhere, however, in the New Testament it has a different meaning attached to it. Paul ranks "heresies" with crimes and seditions ( Galatians 5:20 ). This word also denotes divisions or schisms in the church ( 1 Corinthians 11:19 ). In Titus 3:10 a "heretical person" is one who follows his own self-willed "questions," and who is to be avoided. Heresies thus came to signify self-chosen doctrines not emanating from God ( 2 Peter 2:1 )." -Source: Bible Study Tools