Expungement (also called "expunction") is a court-ordered process in which the legal record of an arrest or a criminal conviction is "sealed," or erased in the eyes of the law. When a conviction is expunged, the process may also be referred to as "setting aside a criminal conviction."
The availability of expungement and the procedure for getting an arrest or conviction expunged, will vary according to several factors, including the state or county in which the arrest or conviction occurred. In some jurisdictions, it's not possible to get an expungement.