bubble boom; ephemeral boom
Refers to an economic boom that is unsustainable and likely to burst, like a bubble. Often used in economic contexts.
Japan was in the grip of a bubble boom in the late 1980s.
Experts warn that this prosperity is nothing more than an ephemeral boom.
バブル景気 is a more common term for 'bubble economy', often specifically referring to Japan's late-1980s asset bubble. 泡沫景気 is a more literary or formal synonym emphasizing the fleeting, insubstantial nature of the boom.
Compound of 泡沫 (ほうまつ, 'bubble, foam') and 景気 (けいき, 'economic conditions, boom'). The metaphor of a bubble conveys something that appears substantial but is easily burst.