Our legal system depends upon the reliability of a person's word—his oath as an officer, his promise as a contractor, his testimony as a witness. Under the common law, conviction of certain crimes so diminished a person's credibility that he permanently forfeited certain of his civil rights, his oath was of no legal value, and he was incompetent to testify in court. Infamy, as this is called, resulted from conviction of felony, or a crime involving willful falsehood. The Fifth Amendment requires presentment or indictment by a grand jury before a person may be tried in federal court for an infamous crime.
In modern political rhetoric, the term "infamy" often means general harm done to a person's reputation, especially as a result of legislative investigations or other governmental action.
Dennis J. Mahoney
Notoriety; condition of being known as possessing a shameful or disgraceful reputation; loss of character or good reputation.
At common law, infamy was an individual's legal status that resulted from having been convicted of a particularly reprehensible crime, rendering him or her incompetent as a witness at a trial. Infamy, by statute in certain jurisdictions, produces other legal disabilities and is sometimes described as civil death.