Yesterday, the Department of Justice filed a memorandum with Judge Bates (D.C. District) re-defining its detention authority. If you'll remember, about a month ago both Judge Bates and Judge Walton of the D.C. District ordered the government to define its detention authority so that it could be used in processing the pending Gitmo habeas petitions.
The memo is careful to not limit the government's power to detain terrorists and says that further development of the "contours of the... bases of detention" will be necessary. The new detention standard is based on the international laws of war instead of the President's power as Commander in Chief as it was under President Bush. The memo says that the law of war and the Authorization for the Use of Military Force encompass al-Qaeda, the Taliban, and all other analogous groups (terrorist organizations), and thus allows the U.S. to detain members of these groups pursuant to the law of war. It goes on to say that the authority extends beyond the battlefields of Afghanistan and reaches those who provide "substantial support" to any of the above named groups. The word "substantial" is also a significant addition to the new definition of detention authority because the old definition under President Bush did not require substantial activity related to terrorism it only required any activity no matter what it was.
I think that those are the most crucial points to take from the new detention definition. For a more in depth discussion check out SCOTUSblog's analysis and also take a look at this DoJ press release.