Science

• Orbital period
  Orbital period
  The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
  
  , a concept in astronomy
• Period (gene)
  Period (gene)
  Period is a gene located on the X chromosome of Drosophila melanogaster. Oscillations in levels of both per transcript and its corresponding protein PER have a period of approximately 24 hours and together play a central role in the molecular mechanism of the Drosophila biological clock driving...
  
  , a gene in Drosophila involved in regulating circadian rhythm
• Period (geology), a subdivision of geologic time
• Periodic function
  Periodic function
  In mathematics, a periodic function is a function that repeats its values in regular intervals or periods. The most important examples are the trigonometric functions, which repeat over intervals of length 2π radians. Periodic functions are used throughout science to describe oscillations,...
  
   and periodical, a function that repeats its values in regular intervals
• Periodic group
  Periodic group
  In group theory, a periodic group or a torsion group is a group in which each element has finite order. All finite groups are periodic. The concept of a periodic group should not be confused with that of a cyclic group, although all finite cyclic groups are periodic.The exponent of a periodic group...
  
   in group theory
• Periodic table
  Periodic table
  The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
  
  , a chart which lists all currently known chemical elements
• Period (periodic table), a horizontal row of the periodic table
• Periodic acid
  Periodic acid
  Periodic acid, or iodic acid is an oxoacid of iodine having chemical formula HIO4 or H5IO6.In dilute aqueous solution, periodic acid exists as discrete hydronium and metaperiodate ions. When more concentrated, orthoperiodic acid, H5IO6, is formed; this dissociates into hydronium and...
  
  , an oxoacid of iodine
• Period (physics), the time taken for one full oscillation, it is the reciprocal of frequency
• Period of orbit
  Orbit (dynamics)
  In mathematics, in the study of dynamical systems, an orbit is a collection of points related by the evolution function of the dynamical system. The orbit is a subset of the phase space and the set of all orbits is a partition of the phase space, that is different orbits do not intersect in the...
  
  
• Period of time
  Periodization
  Periodization is the attempt to categorize or divide time into named blocks. The result is a descriptive abstraction that provides a useful handle on periods of time with relatively stable characteristics...
  
  
• The ring of periods, those numbers which can be expressed as integrals of algebraic differential forms over algebraically defined domains

Language and literature

• Period (punctuation), a punctuation mark indicating the end of a sentence or phrase, specifically, a dot.
• Periodic sentence
  Periodic sentence
  A periodic sentence is a stylistic device employed at the sentence level, characterized as a sentence that is not grammatically complete until the final clause or phrase.-Characteristics:...
  
  , a sentence that is not grammatically complete until its end
• The final book in Dennis Cooper's George Miles cycle of novels

History

• Pisano period
  Pisano period
  In number theory, the nth Pisano period, written π, is the period with which the sequence of Fibonacci numbers, modulo n repeats. For example, the Fibonacci numbers modulo 3 are , 1, 1, 2, 0, 2, 2, 1, 0, 1, 1, etc., with the first eight numbers repeating, so π = 8.Pisano periods are named after...
  
  
• Period piece
  Period piece
  -Setting:In the performing arts, a period piece is a work set in a particular era. This informal term covers all countries, all periods and all genres...
  
   describes creative works set in a particular era

Sports

• Periods in ice hockey, intervals into which a match is divided

Other meanings

• Periodicity, the quality of occurring at regular intervals or periods