Meaning of the word "castles in the air" in English

What does "castles in the air" mean in English? Explore the meaning, pronunciation, and specific usage of this word with Lingoland.

castles in the air

US /ˈkæsəlz ɪn ðə ɛr/
UK /ˈkæsəlz ɪn ðə ɛr/
"castles in the air" picture

Idiom

1.

plans or hopes that are unlikely to come true

Example:
He's always building castles in the air about becoming a millionaire.
Don't waste your time on castles in the air; focus on achievable goals.
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