noun
very short-lived regime; Hundred Days (Napoleon)
Refers to a brief period of rule, often used metaphorically for any short-lived administration. The literal historical reference is Napoleon's return from Elba in 1815.
彼の政権は百日天下に終わった。
His administration turned out to be a very short-lived regime.
ナポレオンの百日天下は歴史
Napoleon's Hundred Days are in the history textbooks.