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The time interval between two successive and similar phases of a regularly occurring event.The period of rotation or of revolution of a planet, etc., is the time to complete one rotation on its axis or one revolution around its primary.

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geologic timescale,a chronological scale of earth's history used to measure the relative or absolute age of any part of geologic time.

Of the numerous timescales, the most common is based on geologic time units, which divide time into eras, periods, and epochs...... Periods are shorter than an era and longer than an epoch.

Periods are of variable length, generally lasting tens of millions of years, with characteristic fossils found preserved in the sediments deposited during the period.

It is also used to designate a characteristic of geologic time, such as the glacial period.

Usually, a period consists of two parts (phrases), each made up of four or eight measures that differ in their cadences (a half cadence in the first phrase and a perfect cadence in the second).(postroenie), in music, a term that is applicable to any section of a musical form that is structurally distinct from adjacent sections.

Usually the term is applied to sections intervening between the main elements of a musical form—for example, sections larger than a phrase but smaller than a sentence.Often, a period is designated by the number of measures it includes (two-measure, four-measure and seven-measure periods, for example).punctuation[Lat.,=point], the use of special signs in writing to clarify how words are used; the term also refers to the signs themselves.In every language, besides the sounds of the words that are strung together there are other features, such as tone, accent, and pauses,.....harmonic motion,regular vibration in which the acceleration of the vibrating object is directly proportional to the displacement of the object from its equilibrium position but oppositely directed......wave,in physics, the transfer of energy by the regular vibration, or oscillatory motion, either of some material medium or by the variation in magnitude of the field vectors of an electromagnetic field (see electromagnetic radiation)......