What descirbes a major difference between the Jewish calender and the gregorian calendar?

the jewish calendar began many centuries before before the Gregorian Calendar.

Jewish answer

The Jewish calendar consists of twelve lunar months. It also keeps in step with the solar year, by adding a thirteenth lunar leap-month seven times every nineteen years. The Gregorian calendar, which sticks to the solar year, ignores the lunar months and does not attempt to keep in step with them.