Which term is used to describe the act of formally charging someone with an offense?

The term that describes the act of formally charging someone with an offense is "indictment." An indictment is a legal document issued by a grand jury, stating that there is enough evidence to charge an individual with a crime. This process is an essential part of the criminal justice system, as it ensures that a person is not charged with a crime without sufficient evidence warranting such action.

In contrast, a summons is a notification to appear in court and is not the formal charging process itself. An arrest involves the apprehension of an individual suspected of committing a crime but does not constitute a formal charge. Incarceration refers to the confinement of an individual in a jail or prison, occurring after a charge has been made, typically following a conviction or when someone has not met bail conditions. Thus, the proper term for the formal charging process is indeed indictment.