Shunki Kōreisai; imperial ancestor worship ceremony on the vernal equinox
Historical term for a former imperial ceremony held on the vernal equinox (春分の日). No longer observed in modern Japan.
See also: 春分の日
The Shunki Kōreisai was an imperial ceremony formerly held on the vernal equinox.
春分の日 is the modern national holiday on the vernal equinox, while 春季皇霊祭 was a specific imperial ancestor worship ceremony held on that day before the post-war separation of state and religion.
Compound of 春季 (spring season), 皇霊 (imperial spirits), and 祭 (festival/ceremony). The term refers to a specific Shinto-style imperial rite that was part of the pre-war state Shinto calendar.