Perhaps the fundamental way to categorize calendars is by their core event that is, what the calendar is based on. The Christian calendar is a solar calendar based on Christ's birth. In religious and traditional secular use, the years are labeled as BC for Before Christ orAD Ahno Domini (in the year of our Lord. More and more, secular uses employ a newer marking system that doesn't recognize that the dates correspond to Christ's birth. They mark the year as BCE or CE, where BCE stands for Before the Common Era, and CE stands the current Era, Common Era, or Christian Era