›a length of time: The study will be carried out over a six-month period.›A period in the life of a person or in history is a particular time during that life or history: The period after World War II was marked by rapid economic growth.›A period is a division of time in an event of fixed length, such as a day at school or a game: There was no scoring in the second period.›physicsA period is the time it takes for one complete repetition of a pattern that repeats. A second is used as the standard unit in most areas of science.›Period costume/dress/furniture is the clothing or furniture of a particular time in history: At the Revolutionary War theme park, everyone was wearing period costumes.