春分 shunbun is Spring equinox. It is the division of seasons.
In Okinawa, it is typically different than mainland Japan, just like shuubun 秋分 (Autumn equinox) is. While in the rest of Japan it may be more typical to visit hometowns and family graves, in Okinawa it is usually just observed at home at the butsudan (buddhist altar), with the typical special Okinawa foods used in most celebrations. The season of shiimii しーみー is just around the corner and it is the customary time to visit, clean and leave offerings at the graves then.
Spring equinox is also part of haru-no-higan 春の彼岸, which just refers to Spring equinox week. (O)higan literally means “the other shore,” meaning the other side of the river which divides the living from the deceased in the afterlife according to Buddhist tradition.
At any rate, it will be a public holiday for me, so I can hopefully enjoy the day off. And likely my sensei will bring in the leftover treats from his family’s celebration.