You could define grace as
Grace is completely undeserved. It is a free gift from God. We can not earn grace.
Ephesians 2:8,9 says, “For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works, lest anyone should boast.”
We can not earn our way to Heaven. We are not saved by doing good works. Good works will follow a person’s salvation, but we are not saved because of them. We are saved because Jesus died on the cross for our sins and the sins of mankind.
In Luke 23:40 a man who had spent his whole life committing crime gave his life to Jesus and received the assurance of eternal life with Christ in Paradise. It was only that simple prayer of faith that saved him, not any good deeds (for he had none) This is the grace and mercy of God in action.
No matter what you have done, you too can receive this grace of God. Tbere is no sin too great that Jesus can’t forgive. Bring your sins to God and with a repentant heart allow Him to wash you clean and give you too the assurance of eternal life in Heaven.