Gregorian calendar vs. Julian calendar

Gregorian calendar

[gri-gawr-ee-uhn kal-uhn-der] / grɪˈgɔr i ən ˈkæl ən dər /

noun

the reformed Julian calendar now in use, according to which the ordinary year consists of 365 days, and a leap year of 366 days occurs in every year whose number is exactly divisible by 4 except centenary years whose numbers are not exactly divisible by 400, such as 1700, 1800, and 1900.

Julian calendar

[jool-yuhn kal-uhn-der] / ˈdʒul yən ˈkæl ən dər /

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.