A virgin is somebody who has not had sex. Once a person has had sex, he or she is no longer a virgin.
The term born-again virgin is used by some to describe a person who is no longer a virgin but is now seeking a new start. Some newly religious people see it as a label for a spiritual renewal and a commitment to only have sex within marriage in future.
Some women feel so pressured by the value placed on virginity, that they are driven to have hymen reconstruction surgery.
Chastity is generally understood as the act of saving yourself sexually for a particular time or person. Some people take a vow of chastity because they believe that it keeps them sexually pure. The vow may be taken for religious reasons.
Celibacy is generally understood as abstaining from sexual activity. Most people practise celibacy for religious reasons.