Wiktionary
blue-sky thinking
alt. 1 (context idiomatic English) Thinking that is not grounded or in touch in the realities of the present. 2 (context idiomatic English) open-minded thinking. n. 1 (context idiomatic English) Thinking that is not grounded or in touch in the realities of the present. 2 (context idiomatic English) open-minded thinking.