Obon (お盆) or just Bon (盆) is a fusion of the ancient Japanese belief in ancestral spirits and a Japanese Buddhist custom to honor the spirits of one's ancestors. This Buddhist–Confucian custom has evolved into a family reunion holiday during which people return to ancestral family places and visit and clean their ancestors' graves when the spirits of ancestors are supposed to revisit the household altars. It has been celebrated in Japan for more than 500 years and traditionally includes a dance, known as Bon Odori.

The festival of Obon lasts for three days; however, its starting date varies within different regions of Japan. When the lunar calendar was changed to the Gregorian calendar at the beginning of the Meiji era, the localities in Japan responded differently, which resulted in three different times of Obon. Shichigatsu Bon (Bon in July) is based on the solar calendar and is celebrated around the 15th of July in eastern Japan (Kantō region such as Tokyo, Yokohama and the Tōhoku region), coinciding with Chūgen. Hachigatsu Bon (Bon in August), based on the lunar calendar, is celebrated around the 15th of August and is the most commonly celebrated time. Kyū Bon (Old Bon) is celebrated on the 15th day of the ninth month of the lunar calendar, and so differs each year, which appears between August 8 and September 7. Exceptions occurred in 2008 and 2019, when the solar and lunar calendar matched, and so Hachigatsu Bon and Kyū Bon were celebrated on the same day. Kyū Bon is celebrated in areas such as the northern part of the Kantō region, Chūgoku region, Shikoku, and Okinawa Prefecture. These three festival days are not listed as public holidays, but it is customary for people to be given leave.