Lunar calendars, like the Chinese and Jewish ones, have leap months for the same reason the Gregorian calendar has leap days: to keep our seasons in line. It’s an entire, extra doubled-up month. However, one would say that year has 13 months, not 12. (At least for the Chinese calendar, not sure about the Jewish one.)
I’m going to be the “um, akchually” person:
Lunar calendars, like the Chinese and Jewish ones, have leap months for the same reason the Gregorian calendar has leap days: to keep our seasons in line. It’s an entire, extra doubled-up month. However, one would say that year has 13 months, not 12. (At least for the Chinese calendar, not sure about the Jewish one.)