Definition - What does Pardon mean?
A pardon is when a government official formally forgives an accused or convicted criminal and relieves him or her of any punishments that he or she would otherwise be subject to.
The President of the United States is one government official who has pardoning power. However, he or she cannot pardon himself/herself in the event of impeachment.
Justipedia explains Pardon
The vast majority of people who are convicted of a crime are never pardoned by a government official, and they are forced to serve their sentences. However, pardons do still happen on occasion.
Pardons can happen if circumstances surrounding the case change, or if cultural changes happen that make the pardon the moral thing to do. However, whether or not a particular person gets pardoned depends on the official that has the power to do so.