Often people refer to a woman’s menstrual cycle as her “period” during the time she is bleeding.

During a menstrual period, a woman bleeds from her uterus (womb) via the vagina. This lasts anything from three to seven days. Each period commences approximately every 28 days if the woman does not become pregnant during a given cycle.

Menstruation is a very complicated process involving many different hormones, the woman’s sex organs and the brain.

A woman’s internal sex organs consist of two ovaries, the Fallopian tubes, the uterus (womb) and the vagina. The ovaries contain the eggs with which the woman is born and, during each period, a single egg will usually ripen and mature due to the action of hormones circulating in the bloodstream.

When the egg is mature it bursts from the ovary and drifts through the Fallopian tube down into the uterus. The lining of the uterus – the endometrium – has been thickened by the action of hormones and made ready to receive the fertilised egg.

If the egg is fertilized and the woman becomes pregnant, it will fasten itself onto the endometrium. If the egg is not fertilized, however, resultant hormonal changes cause the endometrium to slip away and menstruation begins.

Menstrual discharge is composed of the endometrium itself, together with a little fresh blood caused by the breaking of very fine blood vessels within the endometrium as it detaches itself from the inside of the uterus.

The amount of blood lost due to the normal monthly period is usually less than 80ml.

These days, girls begin to menstruate when they are about 10 to 14 years-old. The average age is approximately 12. Women will continue to menstruate until the age of 45 to 55, when menopause begins. A woman will have approximately 500 periods in her lifetime.

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[Middle English periode, from Old French, from Medieval Latin periodus, from Latin perihodos, rhetorical period, from Greek periodos, circuit, peri-, peri-, + hodos, way.]

noun

An interval of time characterized by the occurrence of a certain condition, event, or phenomenon: a period of economic prosperity.

An interval of time characterized by the prevalence of a specified culture, ideology, or technology: artifacts of the pre-Columbian period.

An interval regarded as a distinct evolutionary or developmental phase: Picasso’s early career is divided into his blue period and rose period.

Geology A unit of time, longer than an epoch and shorter than an era.

Any of various arbitrary units of time, especially:

Any of the divisions of the academic day.

Sports & Games A division of the playing time of a game.

Physics & Astronomy The time interval between two successive occurrences of a recurrent event or phases of an event; a cycle: the period of a satellite’s orbit.

An instance or occurrence of menstruation.

A point or portion of time at which something is ended; a completion or conclusion.

The full pause at the end of a spoken sentence.

A punctuation mark ( . ) indicating a full stop, placed at the end of declarative sentences and other statements thought to be complete, and after many abbreviations.

A sentence of several carefully balanced clauses in formal writing.

A metrical unit of quantitative verse consisting of two or more cola.

An analogous unit or division of classical Greek or Latin prose.

Music A group of two or more phrases within a composition, often made up of 8 or 16 measures and terminating with a cadence.

Mathematics

The least interval in the range of the independent variable of a periodic function of a real variable in which all possible values of the dependent variable are assumed.

A group of digits separated by commas in a written number.

The number of digits that repeat in a repeating decimal. For example, = 0.142857142857 . . . has a six-digit period.

Chemistry A sequence of elements arranged in order of increasing atomic number and forming one of the horizontal rows in the periodic table.

adjective

Of, belonging to, or representing a certain historical age or time: a period piece; period furniture.

interjection

Used to emphasize finality, as when expressing a decision or an opinion: You’re not going to the movies tonight, period!

http://www.m-w.com/dictionary/period