A more thorough explanation:

A special grand jury is a group of people who are chosen to sit for at least a month and decide whether to issue indictments in ex parte proceedings. They are similar to a regular grand jury, but are summoned when the regular grand jury has already been discharged or has not been drawn. The special grand jury has limited authority and is usually called for a specific purpose.

For example, a special grand jury may be summoned to investigate possible crimes and develop evidence that is not currently available to the prosecution. This type of grand jury is called an investigative grand jury. Another type of special grand jury is a screening grand jury, whose primary function is to decide whether to issue an indictment.

If the special grand jury decides that there is enough evidence to hold a suspect for trial, it returns a bill of indictment charging the suspect with a specific crime. This is called a true bill. The special grand jury serves two distinct functions: a screening function and an investigational function.

Overall, a special grand jury is an important part of the criminal justice system, as it helps to determine whether there is enough evidence to charge someone with a crime and bring them to trial.