The American Heritage® Dictionary of the English Language: Fourth Edition.
2000.
Three Principal Calendars.
The Gregorian calendar is now in use as the civil calendar
throughout most of the world. The Jewish calendar is the official calendar of
the Jewish religious community. The Islamic calendar is the official calendar
in many Muslim countries. Each calendar listed below begins with the first
month of the year and includes the number of days each month contains. Many
months have a variable number of days, as described below.
