(idiomatic) A length of time during which rules or penalties are waived or deferred.

a school period in which a student has free time, i.e., is not enrolled in a class.

(astronomy) Taking over 200 years to complete an orbit; especially said of comets.

Any of certain species of cicadas, especially in genus Magicicada, which are known for their 17- and 13-year life-cycles, during most of which they develop underground, emerging in large numbers for a short time as large and audible adults, all those emerging in a year constituting a brood.

plural of zero period

plural of notice period

plural of menstrual period

plural of question period

plural of sidereal period

(physics) Half of the period of a wave etc; typically the time taken for part of a wave to be replaced by a similar part that is out of phase.