Nice, basic definition.

I'd only add to make clear that the defendant usually gets no representation before a grand jury. Only the prosecution gets to make their case. That's why it's extremely rare for a grand jury not to indict someone. An article from a few years ago notes: "U.S. attorneys prosecuted 162,000 federal cases in 2010, the most recent year for which we have data. Grand juries declined to return an indictment in 11 of them." That's why there's a famous saying that goes, "if a district attorney wanted, a grand jury would indict a ham sandwich".

Not as nicely succinct as you, but an important point to keep in mind about indictments!