the calendar established by Julius Caesar in 46 b.c., fixing the length of the year at 365 days and at 366 days every fourth year. There are 12 months of 30 or 31 days, except for February (which has 28 days with the exception of every fourth year, or leap year, when it has 29 days). Cf. Gregorian calendar.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.