That a person regrets what they have done
To abandon the like of it immediately
Resolve to never return to it
These are if it is between a person and Allah (the Exalted) and no right is related to it. For if a right is related to it, it is compulsory to fulfil it. If it is a prayer or fast then it is made up, or zakat then it is given. Peoples property is returned if it remains, and compensated if not present, or is absolved of iby them. If the ones whose right it is has passed away then it is given to their inheritors.
As for backbiting, if it does not reach the one who has been backbited the conditions mentioned are sufficient. If however it does reach the person then they ask them to be excused for it. If unable, he asks forgiveness for the person (who was backbited).