An indictment is a formal accusation of a felony, issued by a grand jury based upon a proposed charge, witnesses' testimony and other evidence presented by the public prosecutor (District Attorney). It is the grand jury's determination that there is enough evidence that the defendant committed the crime to justify having a trial voted by a grand jury.
A sealed indictment an indictment that is sealed so that it stays non-public until it is unsealed. This can be done for a number of reasons. It may be unsealed, for example, once the named person is arrested.
Nothing stops indictments..