What is "Otherworld" in the novel, Fairy Tale?

Otherworld is the magic world where fairies live, but it can only be accessed through a portal on one's Day of Birth and Day of Becoming which occurs on one's sixteenth birthday. Dawn leaves Otherworld in order to retrieve Cam and leave Pip, the Brownes' real son, in his place. Morgan and Pip try to conspire to save Cam from leaving, but when Morgan falls in love with Pip, Cam goes to Otherworld to become king as he is the only true heir.