the calendar introduced by Julius Caesar in 46 , in which the ordinary year had 365 days: the months were the same as in the Gregorian, or New Style, calendar now used
See Julian calendar in American Heritage Dictionary 4
The solar calendar introduced by Julius Caesar in Rome in 46 B.C., having a year of 12 months and 365 days and a leap year of 366 days every fourth year. It was eventually replaced by the Gregorian calendar. See Table at calendar.