The Oracles are beings and places that can give prophecies in Greek mythology. Four of them are associated with the god Apollo. There are five of them.
The Five Oracles
Also known as the Pythia, she resides at Camp Half-Blood and gives prophecies to demigods who are about to go on quests. According to tradition, the questers are required to consult the Oracle. No prophecy, no quest.
The author of the Sibylline Books.
Not much is known about this oracle.
This oracle is inhabited by the spirit of Apollo's demigod son Trophonius.
The only oracle not affiliated with Apollo. it is sacred to the titan queen Rhea.