The hymen is a fold of mucous membrane which surrounds or partially covers the external vaginalopening. It forms part of the vulva, or external genitalia. A slang term for hymen is "cherry", as in "losing one's cherry" to mean losing one's virginity. It is not possible to confirm that a woman is a virgin by examining her hymen. In cases of suspected rapeor sexual abuse, a detailed examination of the hymen may be carried out; but the condition of the hymen alone is often inconclusive or open to misinterpretation, especially if the patient has reached puberty. In children, although a common appearance of the hymen is crescent-shaped, many variations are possible.After a woman gives birth she may be left with remnants of the hymen called carunculae myrtiformes or the hymen may be completely absent.
The genital tract develops during embryogenesis, from 3 weeks' gestation to the second trimester, and the hymen is formed following the vagina.
At week seven, the urorectal septum forms and separates the rectum from the urogenital sinus.
At week nine, the müllerian ducts move downwards to reach the urogenital sinus, forming the uterovaginal canal and inserting into the urogenital sinus.
At week 12, the müllerian ducts fuse to create a primitive uterovaginal canal.
At month 5, the vaginal canalization is complete and the fetal hymen is formed from the proliferation of the sinovaginal bulbs (where müllerian ducts meet the urogenital sinus), and becomes perforate before or shortly after birth.
In newborn babies, still under the influence of the mother's hormones, the hymen is thick, pale pink, and redundant (folds in on itself and may protrude). For the first two to four years of life, the infant produces hormones which continue this effect. Their hymenal opening tends to be annular (circumferential).
Past neonatal stage, the diameter of the hymenal opening (measured within the hymenal ring) has historically been proposed to be approximately 1 mm for each year of age.  In children, to make this measurement, a doctor may place a Foley catheter into the vagina and inflate the balloon behind the hymen to stretch the hymenal margin and allow for a better examination. In the normal course of life the hymenal opening can also be enlarged by tampon use, pelvic examinations with a speculum, regular physical activity or sexual intercourse. Once a girl reaches puberty the hymen tends to become so elastic that it is not possible to determine whether a woman uses tampons or not by examining a hymen. In one survey only 43% of women reported bleeding the first time they had sex; indicating that the vagina of a majority of women is sufficiently opened.
The hymen is most apparent in young girls: at this time their hymen is thin and less likely to beredundant, that is to protrude or fold over on itself. In instances of suspected child abuse, doctors use the clock face system to describe the hymenal opening. The 12 o'clock position is below the urethra, and 6 o'clock is towards the anus, with the patient lying on her back.
Infants' hymenal opening tends be redundant (sleeve-like, folding in on itself), and may be combined with annular shaped.
By the time a girl reaches school-age, this hormonal influence has stopped and the hymen becomes thin, smooth, delicate and almost translucent. It is also very sensitive to touch; a physician who needed to swab the area would avoid the hymen and swab the outer vulval vestibule instead.
Prepubescent girls' hymenal opening comes in many shapes, depending on hormonal and activity level, the most common being crescentic (posterior rim): no tissue at the 12 o'clock position; crescent shaped band of tissue from 1–2 to 10–11 o'clock at its' widest around 6 o'clock. From puberty onwards, depending on estrogen and activity levels, the hymenal tissue may be thicker and the opening is often fimbriated or erratically shaped.
After giving birth, the vaginal opening usually has nothing left but hymenal tags (carunculae mytriformes) and is called "parous introitus".
In some cultures the concept of an intact hymen is highly valued at marriage. Some women in Europe undergo hymenoplasty, a restoration of their hymen.
In Korea the word for hymen translates literally as “virgin-skin” and a small industry has grown up around its surgical construction through plastic surgery. In 1994 the Korean Medical Research Center was made to pay compensation to a 40-year-old woman for extreme psychological distress after she lost her hymen during a Pap smear test. The court found that, “it is clear that the hymen is still recognized as a symbol of ‘virginity’ and keeping virginity is valued in society".  Some Korean prenatal clinics offers STD tests with hymenorrhaphy, in order to "free" women from their history of sexual experiences in the past. These surgeries are not approved by the Korean medical association.
In the sixteenth and seventeenth centuries, medical researchers have used the presence of the hymen, or lack thereof, as founding evidence of physical diseases such as "womb-fury". If not cured, womb-fury would, according to these early doctors, result in death.