A month is a standard month or a calendar month. A standard month is 30 standard days. A standard day is 86,400 SI seconds. A calendar month is any month in any year as defined by the UTC time system, and consists of between 28 and 31 calendar days. A calendar day is either 86,399, 86,400, or 86,401 seconds, according to whether a leap second is defined to occur on that day in the UTC time system.
