The vagina (from the Latin for sheath or scabbard) is an anatomical canal in females that is open at the skin in the groin at the vulva and ends at the cervix where it enters the uterus. It runs to the anterior (front) of the rectum and opens next to the anus. It allows sexual intercourse with the male penis, allows the passage of an infant during birth, and the escape of the lining of the uterus during menstruation. Although it is closed in its relaxed state it is malleable enough to easily accommodate a penis for intercourse and, with substantially more difficulty and pain, the passage of the infant. It's capable of producing its own lubricant. It's made of a mix of muscle and fibrous tissue. The outer third of the vagina is very sensitive to touch, but the inner two-thirds does not contain very many nerve endings.
The vagina naturally contains many bacteria and, in most cases, these do not cause infection to the body or any noticeable symptoms. The vagina is capable of cleansing itself and any rinsing or other cleaning is discouraged. The big exception are STDs. The removal of bacteria from the vagina, generally due to excessive cleanliness, can often result in a yeast infection as the vaginal bacteria usually staves off the development of yeast in this environment.