The Hebrew word achor (אָחוֹר) means the back, behind, backwards. It functions as a spatial and temporal reference — describing physical position (the back of something), direction (moving backwards), or temporal reference (what is past, what lies behind). It is related to achar (H310, after, behind) and the broader word family of 'following' and 'coming after.'
In its various uses, achor describes turning the back in retreat or fear, what lies behind, and (temporally) the past. The ancient Hebrew conception of time was often visualized with the past before one's eyes (visible, known) and the future behind one (unseen, unknown) — opposite of the modern Western view.
The imagery of turning backward versus pressing forward is theologically rich. Isaiah 1:4 laments a people who have 'turned their backs' (achor) on the Lord — spiritual apostasy visualized as a physical turning away. Lot's wife is the iconic image of looking backward when God has commanded forward movement (Genesis 19:26).
Paul captures the positive theological principle in Philippians 3:13–14: 'Forgetting what is behind (ta opiso) and straining toward what is ahead, I press on.' The Christian life moves forward in response to the call of Christ — not anchored to past failure, past glory, or past comfort. The call of the Gospel is always forward, always deeper into trust, always toward the goal of knowing Christ.