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• generally, in science, the time taken for one complete cycle of an alternating quantity. The period of oscillation of a wave is the time taken for the wave to complete one wavelength. Period is the reciprocal of the frequency. See amplitude, wavelength, simple harmonic motion.
• in astronomy, Copernicus used period to refer to the time it takes a planet to complete one orbit. See orbital period.
• in mathematics, the period of a function is the length of the interval over which it reappears. See periodic function.
• in chemistry, the term period is often used to mean a periodic table period, a row of the periodic table.
• in geologyGeology (from Greek γ&eta ge "the earth") and λογος logos "word", "reason")) is the science and study of the Earth, its composition, structure, physical properties, history, and the processes that shape it. Geolog to identify named timespans such as the CretaceousThe Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period (about 135 mya) to the beginning of the Paleocene epoch of the Tertiary period (65 mya). The end of the Cretaceous also defines the Period or the NeogeneNeogene Period A unit of geologic time consisting of the Miocene and Pliocene Epochs. The Neogene Period follows the Paleogene Period and is followed by the Quaternary Era. The terms 'Neogene System' and 'Upper Tertiary System' have also been used to desc Period. Periods are generally longer than EpochsThe word epoch can mean either an interval of time, or a particular point in time used as a reference point. In common usage, the term is often used to apply to a period of time when significant related events took place. see also period, era) In geology, and shorter than ErasSee also ERA disambiguation page . An era is a (usually lengthy) period of time with common characteristics. For example: the Biblical era, the Roman era, the Elizabethan era, the Victorian era and the Soviet era. Era is also popularly used to denote the. The term Age is sometimes used more or less interchangeably with Period. See geologic periodIn geology, a period or age is a time span of many millions of years that are assumed to have had similar characteristics. See geologic timescale for a list of geologic Periods and Ages. In general, the duration of Periods/Ages tends to get longer the fur and geologic timescaleA timeline of geologic periods in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. The Earth is thought by geologists to be 4. 6 billion years old. The geologic or "deep" time of Earth's past has been or to put this in perspective.
• the word period is often used in to refer to discrete portions of human historyHistory is often used as a generic term for information about the past, such as in "geologic history of the Earth". When used as the name of a field of study, history refers to the study and interpretation of the record of human societies. The term histor, which are also often called ages or eras (see also era). Historical periods include the following: Prehistory, Stone age, Bronze Age, Ice age, Iron Age, Ancient history, Middle Ages, Dark age, Golden age, Edwardian period, Elizabethan era, Victorian era, Information Age, Little Ice Age, Viking Age, The Age of Reason.
• in education, a short period of teaching in a particular subject. See lesson.
• Period is also used in a more vague fashion by interior decorators and designers in the form of "period" decorating, or "period" furniture, which may be from any historical period, or even "old-fashioned".

Further meanings less connected with time:

• in rhetoric, refers to well-balanced sentences. See period (rhetoric).
• in writing, a period is another name for the full stop punctuation sign: "."
• also in writing, a period can refer to any dot.
• a colloquial term for menstruation.
• in music a period is in some ways equivalent to a period in writing: it closes a phrase of music, though the "period" may also be the cadence or close of the phrases.