Here you'll find the laws of each state that deal with the process of hiding or erasing criminal records. The process is different in every state. Expungement or sealing of criminal records is when someone's criminal history or background is erased or hidden so that, except in very limited circumstances, no one can ever find out that person was ever arrested for or convicted of crime.
Some states don't allow records to be expunged or sealed, while others limit it to juvenile records, arrests records where there's no conviction, or first-time convictions for minor, non-violent crimes. Also, some states use the terms "expungement" and "sealing" as meaning the same thing. Other states use their original meanings: "Sealing" means hiding the records away from the public, while "expungement" means the complete destruction of the records. Some states don't use these terms at all, but rather use "removal," "destruction," "expunction" or some other term.
Anyone thinking of trying to have a criminal record expunged or sealed needs to understand what may be expunged, as well as when and how.