In a generic sense, atonement is the act of making amends or reparation for a wrong or injury; it is to reconcile.
When considering God, atonement then becomes the action by which we are made right with him for the wrong things we have done.
Key verse about Atonement: For seven days make atonement for the altar and consecrate it. Then the altar will be most holy, and whatever touches it will be holy (Exodus 29:37, NIV)
A lifelong student of the Bible, Peter DeHaan, PhD, wrote the 700-page website ABibleADay.com to encourage people to explore the Bible. His main blog and numerous books urge Christians to push past the status quo and reconsider how they practice their faith in every area of their lives.