A common year is a common type of calendar year. It has exactly 365 days and so is not a leap year. More generally, it is a calendar year without intercalation.
A common year of 365 days has exactly 52 weeks and one day, so consequently the next new year is one day of the week later.
In the Gregorian calendar, 303 of every 400 years are common years. By comparison, in the Julian calendar, 300 out of every 400 years were common years.
Plural 
common year (plural common years)

A common year is a year that is not a leap year. In the Gregorian Calendar a common year has 365 days. This means a common year has 52 weeks and one day. So if a certain year started on a Monday, the following year will start on a Tuesday. Stated differently, a common year always begins and ends on the same day of the week. (For example, in 2009, both January 1 and December 31 fell on a Thursday.)
In the Gregorian calendar, 303 out of every 400 years are common years. In the Julian calendar, 300 out of every 400 years were common years. All the other years are special and known as leap years.
These are the 12 months in a year.
There are 7 months with 31 days. There are 4 months with 30 days. There is 1 month with 28 days.
