periods

Periods is a term that has several distinct meanings across different fields and contexts. In writing, a period is the punctuation mark used to indicate the end of a declarative sentence. It is a small circle or dot placed at the end of a sentence in many languages that use the Latin alphabet. The term also appears in abbreviations, for example Dr. for doctor, and as part of decimal notation in some locales.

In biology and medicine, a menstrual period refers to the part of the female reproductive cycle when the lining of the uterus is shed, resulting in bleeding through the vagina. This typically lasts two to seven days, and is usually accompanied by hormonal changes that may cause physical or emotional symptoms. The duration and intensity vary among individuals and across cycles, and patterns often change with age, health, and lifestyle.

Geologically, a period is a subdivision of rock time within an era, characterized by distinct fossil assemblages and rock formations. Examples include the Jurassic and the Cretaceous periods. Periods span millions of years and help scientists organize the history of the Earth.

In mathematics and related disciplines, the period of a function describes the length of one complete cycle after which the function repeats its values. In music and rhythm, a period can refer to a regular interval of time or a measure of the tempo. The term is also used in daily life to describe a defined stretch of time, such as a class period in a school timetable.