a length or portion of time

he had long periods of depression

the period 1977–85

the training period is between 16 and 18 months

the ale will be available for a limited period

the interval of time between successive occurrences of the same state in an oscillatory or cyclic phenomenon, such as a mechanical vibration, an alternating current, a variable star, or an electromagnetic wave

a flow of blood and other material from the lining of the uterus, occurring in non-pregnant women at intervals of about 28 days between puberty and the menopause and typically lasting for a few days

she's got her period

period pains

a punctuation mark (.) used at the end of a sentence or an abbreviation; a full stop

a set of elements occupying a horizontal row in the periodic table

a complex sentence, especially one consisting of several clauses, constructed as part of a formal speech or oration