Why are two months the same in a year?

A leap month is a way to set a leap month in a calendar. In Asia (especially in China), leap month refers to one month added every leap year in the lunar calendar (in order to coordinate the contradiction between the tropic year and the lunar year and prevent the lunar year from being out of touch with the tropic year and the four seasons, 1 leap and 19 leap are set every two to three years). Sometimes, a leap month also refers to a month that includes a leap day in a leap year (especially in February of a leap year in the Gregorian calendar).