태음력, or the lunar calendar, is a calendar system based on the phases of the moon. It consists of 12 months, each beginning with the new moon, and typically has 354 days in a year. To align with the solar year, an extra month is added approximately every three years, creating a leap year. This calendar is used in various cultures, including 한국 (Korea), 중국 (China), and 일본 (Japan), for traditional festivals and agricultural activities. Important holidays, such as 설날 (Lunar New Year) and 추석 (Chuseok), are determined by the lunar calendar, reflecting its cultural significance.