雨後の筍
(Ugo no takenoko; “Bamboo shoots after the rain”)

Definition:

The same thing, or similar things, popping up one after another. Repetition. Recurrence. Like a profusion of bamboo shoots sprouting after the rain. Like mushrooms after the rain, in Western parlance.

Breakdown:

This simple idiom is a noun phrase. It begins the adverbial noun 雨後 (ugo), “after the rain.” The associative particle の (no) marks it as connected to and modifying the noun 筍 (takenoko), “bamboo shoot.”

Notes:

Apparently some people interpret this phrase as referring to speedy growth, but this is considered an error.

Takenoko may also be written using better-known characters, as 竹の子.

Example sentence:

「最近、汚職スキャンダルが雨後の筍みたいに頻繁に顕れているような気がする」

(“Saikin, oshoku sukyandaru ga ugo no takenoko mitai ni hinpan ni arawareteiru you na ki ga suru.”)

[“I feel like recently, corruption scandals have been cropping up nonstop, like mushrooms after the rain.”]