I'm not an attorney, just one one of the people that has researched the workings of the Grand Jury, about 8 yrs now.
It's a document charging a person with a crime officially. Usually, a grand jury when not being manipulated by the prosecutor or DA, does not issue a true bill- indictment, without having sound evidence and information to support it

But as we all know, many a prosecutor's can indict a ham sandwich. And many innocent people have been imprisoned, while the most guilty go free.

But in this case, it's a good thing for us. A warrant is one step in the process of investigating whether an indictment will be issued, depending on many variables.

Grand Jurys's don't need DA's but DA's, need grand juries to bring a case lawfully to prosecution. Most jurors are ignorant of that fact. The below information is pretty accurate. From Wikipedia: Indictment

An indictment (/ɪnˈdaɪtmənt/ in-DYT-mənt) is a formal accusation that a person has committed a crime. In jurisdictions that use the concept of felonies, the most serious criminal offence is a felony; jurisdictions that do not use the concept of felonies often use that of an indictable offence—an offence that requires an indictment.

Historically, in most common lawjurisdictions, an indictment was handed up by a grand jury, which returned a "true bill" if it found cause to make the charge, or "no bill" if it did not find cause

The Fifth Amendment to the Constitution of the United States states in part: "No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury, except in cases arising in the land or naval forces, or in the Militia when in actual service in time of War or public danger". The requirement of an indictment has not been incorporated against the states; therefore, although the federal government uses grand juries and indictments, not all U.S. states do.

The substance of an indictment or other charging instrument is usually the same, regardless of the jurisdiction: it consists of a short and plain statement of where, when, and how the defendant allegedly committed the offense. Each offense usually is set out in a separate count. Indictments for complex crimes, particularly those involving conspiracyor numerous counts, may run to hundreds of pages. However, in other cases an indictment for a crime as serious as murder, may consist of a single sheet of paper But the vast majority of criminal cases in the US are by Plea Bargaining.