As others have replied, Cherry Valance is a beautiful red-haired cheerleader. Ponyboy is absolutely taken with her. She is with a friend, Marcia, when Ponyboy and Johnny first meet her, and Ponyboy notes that although Marcia too is "cute," Cherry is the real stunner. She can be regarded as the main female character in the novel.
Ponyboy does seem to be genuinely attracted to Cherry, although he doesn't really say so directly. But it isn't just her physical characteristics that attract him. He also likes her for being considerate and sensitive. She is a Soc girl but she shows no condescension whatsoever towards Greasers like Ponyboy. In fact she strikes up an immediate rapport with both Ponyboy and Johnny. All three are similarly thoughtful and sensitive - unlike practically everyone else in the novel, except maybe Soda, to some degree.
Cherry forms an important link between the Socs and Greasers. She helps Ponyboy to realize that underneath all the external differences, Socs and Greasers are really the same: they're all human.