A 24-hour period is a unit of time that is equal to one DAY and night, or 24 hours. It is commonly used to measure the length of a DAY, as well as to measure the amount of time between two events. The term '24-hour period' is often used interchangeably with the term 'DAY, ' although technically they are not the same. The crossword solution for this term is 'days, ' which is an appropriate answer since days are composed of 24-hour periods.