Chindogu are inventions that are not really useful but are at the same time, not completely without use. They make sense, but you’d never use them. They are also, as a result, often really funny.
This chindogu article gives some great examples while also sharing the 10 tenets of what makes chindogu, chindogu. Things like: there must be the spirit of anarchy — they represent freedom of thought and action. And they must exist — just the idea isn’t enough, they must be made.
Apparently, the selfie-stick was invented as chindogu but failed as people evidently actually found it useful — though you can still see why it might have started as chindogu.
More genius from the Japanese: Tsundoku