A month is a unit of time used with calendars that is approximately as long as a natural orbital period of the Moon, which is about 29.5 days. The traditional concept of a month arose with the lunar cycle, and calendars such as the Gregorian calendar divide the year into 12 months that individually last between 28 and 31 days. The names of the months were Anglicized from various Latin names and events important to Rome, except for the months 9–12, which are named after the Latin numerals (septem, octo, novem, decem) . The only month with a variable number of days is February, which has 29 days during a leap year and 28 days otherwise.
In addition to the synodic month, which is the most familiar lunar cycle, there are other types of lunar months, such as the draconic month and the anomalistic month, which are defined based on the Moons orbit around the Earth. A month can also refer to an indefinite, usually extended period of time.
