The hymen is a thin piece of tissue around the vaginal opening. It’s sometimes called the maidenhead or cherry.
·        It is not a membrane that blocks the vaginal opening, as some think. It’s open in the middle. This allows the menstrual blood to pass from the vagina.
·        The shape, size and thickness of this ring of tissue differ. It can be completely absent at birth, but also stretch across most of the vaginal opening. The central opening can be round or elongated.
·        This tissue can tear easily without having sex or be elastic enough to permit a penis to enter without tearing. So nobody can determine by physical examination whether a girl is a virgin or not.

What’s an imperforate hymen?
Does a virgin always bleed on the wedding night?

See also: I’ve masturbated with a candlestick. Am I still virgin or have I
deflowered myself?