1. An interval of time characterized by the occurrence of a certain condition, event, or phenomenon: a period of economic prosperity.

2. An interval of time characterized by the prevalence of a specified culture, ideology, or technology: artifacts of the pre-Columbian period.

3. An interval regarded as a distinct evolutionary or developmental phase: Picasso's early career is divided into his blue period and rose period.

4. Geology A unit of time, longer than an epoch and shorter than an era.

5. Any of various arbitrary units of time, especially:

   1. Any of the divisions of the academic day.

   2. Sports & Games A division of the playing time of a game.

   3. A metrical unit of quantitative verse consisting of two or more cola.

   4. An analogous unit or division of classical Greek or Latin prose.

   5. The least interval in the range of the independent variable of a periodic function of a real variable in which all possible values of the dependent variable are assumed.

   6. A group of digits separated by commas in a written number.

   7. The number of digits that repeat in a repeating decimal. For example, ¹/₇ = 0.142857142857 . . . has a six-digit period.

6. Physics & Astronomy The time interval between two successive occurrences of a recurrent event or phases of an event; a cycle: the period of a satellite's orbit.

7. An instance or occurrence of menstruation.

8. A point or portion of time at which something is ended; a completion or conclusion.

9. The full pause at the end of a spoken sentence.

10. A punctuation mark ( . ) indicating a full stop, placed at the end of declarative sentences and other statements thought to be complete, and after many abbreviations.

11. A sentence of several carefully balanced clauses in formal writing.

12. 1. A metrical unit of quantitative verse consisting of two or more cola.

    2. An analogous unit or division of classical Greek or Latin prose.

    3. The least interval in the range of the independent variable of a periodic function of a real variable in which all possible values of the dependent variable are assumed.

    4. A group of digits separated by commas in a written number.

    5. The number of digits that repeat in a repeating decimal. For example, ¹/₇ = 0.142857142857 . . . has a six-digit period.

13. Music A group of two or more phrases within a composition, often made up of 8 or 16 measures and terminating with a cadence.

14. Mathematics

    1. The least interval in the range of the independent variable of a periodic function of a real variable in which all possible values of the dependent variable are assumed.

    2. A group of digits separated by commas in a written number.

    3. The number of digits that repeat in a repeating decimal. For example, ¹/₇ = 0.142857142857 . . . has a six-digit period.

15. Chemistry A sequence of elements arranged in order of increasing atomic number and forming one of the horizontal rows in the periodic table.

Synonyms: These nouns refer to a portion or length of time. Period is the most general: a short waiting period; a difficult period of my life; the Romantic period in music.
Epoch refers to a period regarded as being remarkable or memorable: "We enter on an epoch of constitutional retrogression" (John R. Green).
An era is a period of time notable because of new or different aspects or events: "How many a man has dated a new era in his life from the reading of a book" (Henry David Thoreau).
An age is usually a period marked by a distinctive characteristic: the age of Newton; the Iron Age.
A term is a period of time to which limits have been set: Senators are elected for a term of six years.

Word History: Many may have wondered why the word period has the sense "punctuation mark ( . )" as well as several senses having to do with time. The answer to this question lies in one of the senses of the Greek word periodos from which our word is descended. Periodos, made up of peri-, "around," and hodos, "way," in addition to meaning such things as "going around, way around, going around in a circle, circuit," and with regard to time, "cycle or period of time," referred in rhetoric to "a group of words organically related in grammar and sense." The Greek word was adopted into Latin as perihodos, which in the Medieval Latin period acquired a new sense related to its use in rhetoric, "a punctuation mark used at the end of a rhetorical period." This sense is not recorded in English until 1609, but the word had already entered English as a borrowing from Old French in the sense "a cycle of recurrence of a disease," first being recorded in a work written around 1425.