A common year is a common type of calendar year. In the Gregorian calendar, a common year has exactly 365 days and so is not a leap year. More generally, it is a calendar year without intercalation.
A common year of / days has exactly 52 weeks and one day, so consequently the next new year is one day of the week later. Stated differently, a common year always begins and ends on the same day of the week. (For example, in 2010, both January 1 and December 31 fell on a Friday.)
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.
In the Lunisolar calendar and the Lunar calendar, a common year has 354 days.