A pardon is a government decision to allow a person who has been convicted of a crime, to be free and absolved of that conviction, as if never convicted.
It is typically used to remove a criminal record against a good citizen for a small crime that may have been committed during adolescence or young adulthood.
Although procedures vary from one state to another, the request for a pardon usually involves a lengthy period of time of unreproachable behavior and a reference check.
Generally speaking, the more serious the crime, the longer the time requirement for excellent behavior.
In the USA, the power to pardon for federal offenses is rarely used and belongs to the President.