To backslide is to turn back or away from faithful obedience to God, whether doctrinally or morally. The term may describe partial or complete religious apostasy, though one occurrence translated “backslider” can simply mean a person who does not adhere to what is right.
The prophets use backsliding especially of Israel’s forsaking Yahweh within the covenant relationship. Israel’s idolatry is portrayed as unfaithfulness to Yahweh, her husband. The New Testament also uses the language for departure from the faith.
The underlying expressions mean turning back, rebellion, stubbornness, or apostasy. The prophetic image compares Israel’s unfaithfulness with violation of a marriage bond.