The term 'PERIOD OF 24 HOURS' can be represented by the crossword solution DAY, which is a three-letter word. A DAY is a unit of time that is typically defined as the time it takes for one rotation of the Earth relative to the Sun. It is commonly used to measure the length of time between two events or occurrences. The length of a DAY is usually 24 hours, although this can vary depending on the time of year and location.