(biology) The period, after excitation, during which a membrane recovers its polarization and is not able to respond to a second stimulus.

(music) the musical period of time following the Classical period falling between about 1820 and the start of the twentieth century.

(politics, government) In Canadian federal and provincial parliaments, a period of regularly scheduled time in the lower chamber during which members of the official opposition party and other members may direct questions to the prime minister and to cabinet ministers concerning affairs of state.

(chemistry) The principle that chemical properties of the elements are periodic functions of their atomic numbers

(Internet) The period of time at the launch of a new top-level domain or second-level domain during which trademark owners may register domain names containing their trademarks (to prevent cybersquatting).

(historical) The history of Japan covering the years from AD 710 to 794. Empress Gemmei established the capital of Heijō-kyō (present-day Nara).

(education) A high school class that is offered early in the morning, before the scheduled start of the school day.

plural of menstrual period

(astronomy) sidereal orbital period / (astronomy) sidereal rotation period

(astronomy) The apparent orbital period of a planet as seen from Earth.