From the U.S. Attorney's Manual:

9-11.151 Advice of "Rights" of Grand Jury Witnesses

It is the policy of the Department of Justice to advise a grand jury witness of his or her rights if such witness is a "target" or "subject" of a grand jury investigation. See the Criminal Resource Manual at 160 for a sample target letter.

A "target" is a person as to whom the prosecutor or the grand jury has substantial evidence linking him or her to the commission of a crime and who, in the judgment of the prosecutor, is a putative defendant....

A "subject" of an investigation is a person whose conduct is within the scope of the grand jury's investigation.

Here's the Department of Justice's sample target letter.

This letter is supplied to a witness scheduled to appear before the federal Grand Jury in order to provide helpful background information about the Grand Jury. The Grand Jury consists of from sixteen to twenty-three persons from the District of ___. It is their responsibility to inquire into federal crimes which may have been committed in this District.

As a Grand Jury witness you will be asked to testify and answer questions, and to produce records and documents. Only the members of the Grand Jury, attorneys for the United States and a stenographer are permitted in the Grand Jury room while you testify.

We advise you that the Grand Jury is conducting an investigation of possible violations of federal criminal laws involving, but not necessarily limited to *. You are advised that the destruction or alteration of any document required to be produced before the grand jury constitutes serious violation of federal law, including but not limited to Obstruction of Justice.

You are advised that you are a target of the Grand Jury's investigation. You may refuse to answer any question if a truthful answer to the question would tend to incriminate you. Anything that you do or say may be used against you in a subsequent legal proceeding. If you have retained counsel, who represents you personally, the Grand Jury will permit you a reasonable opportunity to step outside the Grand Jury room and confer with counsel if you desire.

That being said, the use of the word "target letter" by reporters and others would be appropriate if, for example, after Judith Miller's testimony Fitzgerald was offering Libby or others the chance to come back before the grand jury and give their final version. Had their classification changed from "subject" to "target" because of her testimony, he would have to advise them of that before they testified.

But, it sounds like this grand jury is complete, and notifications are going out to various lawyers that their clients are being or have been indicted, and as a courtesy, they can bring their clients in rather than face the humiliation of an arrest at home or work.