Month is a unit of time, used with calendars, that is approximately as long as a natural period related to the motion of the Moon.
The traditional concept arose with the cycle of Moon phases; such months (lunations) are synodic months and last approximately 29.53 days.
The term "month" also refers to:
1. A period of about 4 weeks or 30 days
2. One of the twelve divisions of a calendar year
3. In finance, a billing cycle period