limitless budget; open-ended budget
Refers to a budget without a fixed ceiling, often used in economic or political contexts. The term 青天井 (blue sky ceiling) metaphorically suggests no upper limit.
The government implemented economic measures with an open-ended budget.
青天井 is the core metaphor meaning 'blue sky ceiling' or 'no upper limit'. 青天井予算 specifically applies this to a budget.
Compound of 青天井 (あおてんじょう, 'blue sky ceiling', i.e., no upper limit) and 予算 (よさん, 'budget'). The exact historical derivation is uncertain, but the phrase is conventionally associated with limitless spending.