A pardon is the forgiveness of a crime and cancellation of penalty and is usually granted by the President. A reprieve is the postponement of punishment, often with a view to a pardon. Pardons are sometimes offered to those wrongfully convicted of a crime. In some jurisdictions, accepting such a pardon is also admission of guilt, so there are times the pardon is refused. Wrongful conviction is often handled by appealing, but a pardon can be offered (when undisputed) in order to avoid the costs of a retrial.
Here on LawServer you’ll find relevant state laws about pardon, and related legal Questions & Answers.