1. A rather large interval of time that is meaningful in the life of a person, in history, etc., because of its particular characteristics.
2. Any specified division or portion of time: poetry of the period from 1603 to 1660.
3. A round of time or series of years by which time is measured.
4. A round of time marked by the recurrence of some phenomenon or occupied by some recurring process or action.
5. The point of completion of a round of time or of the time during which something lasts or happens.
6. A specific length of time during school hours that a student spends in a classroom, laboratory, etc., or has free.
7. Any of the parts of equal length into which a game is divided.
8. The time during which something runs its course.
9. The present time.
10. The point or character (.) used to mark the end of a declarative sentence, indicate an abbreviation, etc.; a full stop.
11. A full pause, as is made at the end of a complete sentence; a full stop.
12. A sentence; especially, a well-balanced, impressive sentence.
13. A term used to indicate an occurrence of menstruation.
14. A time of the month during which menstruation occurs.
15. The basic unit of geologic time, during which a standard rock system is formed.
16. The duration of one complete cycle of a wave or oscillation; the reciprocal of the frequency.
17. A musical division of a composition, usually a passage of eight or sixteen measures, complete or satisfactory in itself, commonly consisting of two or more contrasted or complementary phrases ending with a conclusive cadence.
18. In astronomy, "a period of rotation"; the time in which a body rotates once on its axis or "a period of revolution"; the time in which a planet or satellite revolves once about its primary.
19. Noting, pertaining to, evocative of, imitating, or representing a historical period or the styles which are current during a specific period of history; such as, period costumes; a period play.
20. Used by a speaker or writer to indicate that a decision is irrevocable or that a point is no longer discussable: "I forbid you to leave, period."
21. Etymology: A "course or extent of time", from Modern Latin periodus, "recurring portion, cycle", from Latin periodus, "a complete sentence"; also "cycle of the Greek games" from Greek periodos, "rounded sentence, cycle, circuit, period of time"; literally, "going around", from peri-, "around" plus hodos, "a going, a way, a journey".

Sense of "repeated cycle of events" led to that of "interval of time". Meaning "dot marking end of a sentence" first recorded in 1609, from a similar use in Modern Latin. Sense of "menstruation" dates from 1822. Educational sense of "portion of time set apart for a lesson" is from 1876. Used in the sporting sense is attested from 1898.

Heavy and prolonged precipitation during the Ice Age in a normally dry or semi-arid area of land with little evaporation: In her biology class at school, Linda learned that the extreme rainfall during the Pleistocene epoch was known as the pluvial period, which caused an expansion of vegetation and created lakes: for example, Lake Lahonta in Nevada, USA, and Lake Bonneville in Utah, USA.

An intermission or pause for relaxation: "Jim's uncle says that he can accomplish much more after he has a rest period each day."

The time it takes for a planet or satellite to make one complete circuit of its orbit (360°) relative to the stars: "The Earth's sidereal period, or sidereal year, is equal to 365.2564 mean solar days."