noun
minor festival; off-year festival
A smaller festival held in years when the main festival (本祭り) does not take place, often with reduced scale or events.
See also: 本祭り
今年は本祭りがないので、代わりに陰祭りが行われます。
Since the main festival isn't held this year, a minor festival will take place instead.
陰祭りでは、神輿の数が少
During the off-year festival, there are often fewer portable shrines.
本祭り is the main, full-scale festival held in certain years, while 陰祭り is the smaller substitute held in off-years.
陰 (kage, 'shadow' or 'hidden') + 祭り (matsuri, 'festival'), referring to a festival held in the 'shadow' of the main one.