When Holden finally realizes that he is only running from himself, and to go through with his initial plan would drag Phoebe down with him. He decides to just go home.
When the protagonist's sister asks him what he wants to be when he grows up, he responds by quoting a lyric from a song about being a catcher in the rye. And that's how the book has its title.
Holden Caulfield wants to the catcher in rye simply because he understands his own mental as well as social predicament that he suffers from and he wants to protect other children from such traumas....