noun
Collections of the Twenty-One Eras; twenty-one imperial waka anthologies
Refers to the twenty-one waka collections compiled by imperial command from the early Heian period to the early Muromachi period, starting with the Kokin Wakashū and ending with the Shinshoku Kokin Wakashū.
See also: 勅撰和歌集
二十一代集は、勅撰和歌集の総称として知られている。
The Nijūichidaishū is known as the collective term for the imperial waka anthologies.
勅撰和歌集 is the broader category of imperial waka anthologies, while 二十一代集 specifically refers to the set of twenty-one such collections compiled up to the early Muromachi period.
From 二十一 (twenty-one) + 代 (era, generation) + 集 (collection), referring to the twenty-one imperial waka anthologies.