1. A length or portion of the time.
2. The interval of time between successive occurrences of the same state in an oscillatory or cyclic phenomenon, such as mechanical vibration, an alternating current, a variable star, or an electromagnetic wave.
3. Flow of blood and other material from the lining of the uterus, lasting for a few days and occurring in sexually mature women who are not pregnant at intervals of about one lunar month until the menopause.
4. A punctuation mark (.) used at the end of a sentence or an abbreviation; a full stop.
5. A set of elements occupying a horizontal row in the periodic table.
6. Belonging to or characteristic of a past historical time, especially in style or design.
Plural noun: Periods.
1. They covered a period of 15 years.
2. Today my Science period was of 55 minutes.