The Oracle of Secrets, also known as Farore, is an Oracle named after the Goddess of Courage. In The Legend of Zelda: Oracle of Seasons and Oracle of Ages, Farore is in the Hall of Secrets. She's the sister of Din and Nayru as well. Though she doesn't sing or play instruments as Nayru does, or dance as Din does, she helps you out with the secrets you obtain through both Seasons and Ages.
The Legend of Zelda: Mystical Seed of Courage
Farore was going to be the main oracle of The Legend of Zelda: Mystical Seed of Courage. The game was dismissed due to linking errors. So instead of wasting her, they gave her a minor role in both Seasons and Ages. Either way, it seems The Legend of Zelda: Mystical Seed of Courage was a combination of Seasons and Ages and was going to use the same type of time loss system as the Temple of the Ocean King in The Legend of Zelda: Phantom Hourglass. This explains her second name being the Oracle of Hours. But none of this was official, and the idea seemed to be ditched until The Legend of Zelda: Phantom Hourglass was released with the time loss system.