Anno Mundi (Latin: "in the year of the world"), abbreviated as AM or A.M., refers to a Calendar era based on the biblical creation of the world. Numerous efforts have been made to determine the biblical date of Creation, yielding varying results. Besides differences in interpretation, which version of the Bible is being referenced also impacts on the result. (see Dating creation)
The Hebrew calendar era is used within the Jewish communities for religious and other purposes; and the Byzantine calendar has been in general use at one time in the Orthodox Churches and several Eastern European countries.
Two dominant dates for creation using such models exist, about 5500 BC and about 4000 BC. These were calculated from the genealogies in two versions of the Bible, with most of the difference arising from two versions of Genesis. The older dates are based on the Greek Septuagint. The later dates are based on the Hebrew Masoretic text. Patriarchs from Adam to Terah, the father of Abraham, are said to be older by as much as 100 years or more when they begat their named son in the Septuagint than they were in the Hebrew or the Vulgate (Genesis 5, 11). The net difference between the two genealogies of Genesis was 1466 years (ignoring the "second year after the flood" ambiguity), which is virtually all of the 1500-year difference between 5500 BC and 4000 BC.
Read more about Anno Mundi: Jewish Tradition, Greek Tradition, Roman Tradition, Muslim Tradition