expression
distracted; absent-minded; physically present but mentally elsewhere
Describes a state where one's body is present but the mind is wandering; often used when someone is not paying attention or is preoccupied.
授業中、彼は心ここにあらずで、窓の外を見ていた。
During class, he was distracted and staring out the window.
会議で心ここにあらずの様子だった。
He seemed absent-minded at the meeting.
Both mean being distracted or not fully present. 心ここにあらず emphasizes a disconnect between body and mind, while 上の空 often implies a dreamy, inattentive state.
ぼんやり is a more general term for being spaced out or vague, whereas 心ここにあらず specifically conveys that one's mind is elsewhere despite physical presence.
A classical Japanese expression literally meaning 'the heart/mind is not here'. It originates from a phrase in Chinese literature and has been used in Japanese for centuries to describe mental absence.