User blog comment:Captainkirk90/other Giants/@comment-82.151.153.118-20111121112712/@comment-3146930-20111121145404

They mean that the giants that have appeared so far are the rivals of the parents of the 7 prophecy demigods (also the 7 Olympian Week gods). So far we have seen the rivals of Zeus, Athena, Hades, and Poseidon, so there are going to be giants for Hephaestus, Aphrodite, and Ares