Period

The period, known as a full stop in British English, is a punctuation mark used to end declarative sentences and to abbreviate words. It is a single dot placed at the end of a sentence and appears on keyboards and in printed text. In writing it signals a pause and helps clarify meaning. In computing and mathematics, the symbol can serve as a decimal separator in some contexts and appears in web addresses and file names as a dot.

The term period also denotes a length of time with defined start and end points. Periods can describe historical epochs (for example, the Renaissance), calendar segments (the Victorian period), or any interval with boundaries. In science it extends to orbital periods, which measure the time a body takes to complete an orbit.

Geology uses the term as a subdivision of geologic time within eras. Geological periods, such as the Cambrian and Jurassic, are defined by distinctive rock layers and fossil assemblages. Boundaries are established by stratigraphic convention and coordinated by international bodies such as the International Commission on Stratigraphy.

In human biology, a menstrual period is part of the reproductive cycle. It involves shedding of the uterine lining and vaginal bleeding when pregnancy does not occur. Typical cycle length is about 28 days, with bleeding lasting roughly 3 to 7 days. Variation is common among individuals.

Other common uses include a musical period, which is a complete musical idea usually built from two phrases, and the notion of a class or work period as a defined block of time for a particular activity.