Year zero
Historians have never included a year zero. This means that between, for example, and , there are 999 years: 500 years BC, and 499 years AD preceding 500. In common usage "anno Domini" 1 is preceded by the year 1 BC, without an intervening year zero. Neither the choice of calendar system (whether Julian or Gregorian) nor the era ("Anno Domini" or Common Era) determines whether a year zero will be used. If writers do not use the convention of their group (historians or astronomers), they must explicitly state whether they include a year 0 in their count of years, otherwise their historical dates will be misunderstood.
Characters and organizations in Year Zero
The Solutions Backwards Initiative is a group of students, professors, and IT specialists who devise a method of, and succeed in, sending information back through time. The information sent back is theorized to be the websites that are connected to "Year Zero". However, the data they send back through time gets somewhat corrupted, causing the garbled appearance of all of the sites in the "Year Zero" universe.