something extremely rare; something unexpected to exist
Idiomatic expression literally meaning 'jellyfish bones'; used to describe something so rare or unlikely that it is almost unimaginable. Rare term.
Him being late is like finding jellyfish bones — something you'd never expect.
A story that convenient is like jellyfish bones — exceedingly rare.
Rare idiomatic expression; the kanji 水母 is an uncommon spelling for くらげ (jellyfish).
Kana spelling is more common and avoids the rare kanji 水母.
The phrase literally means 'jellyfish bones'. Since jellyfish have no bones, the expression is used to refer to something that is extremely rare or unexpected. The exact origin is uncertain, but it is a traditional Japanese idiom.