Chastity means the successful integration of sexuality within the person and thus the inner unity of man in his bodily and spiritual being. Sexuality, in which man's belonging to the bodily and biological world is expressed, becomes personal and truly human when it is integrated into the relationship of one person to another, in the complete and lifelong mutual gift of a man and a woman.
The virtue of chastity therefore involves the integrity of the person and the integrality of the gift.
Source: Catechism of the Catholic Church (Vatican.va)