inattention; absent-mindedness; spacing out
Describes a state where one's mind is elsewhere, not paying attention to the immediate surroundings or conversation. Often used with する or だ.
During class, he was spacing out and looking out the window.
話しかけても上の空で、返事がなかった。
Even when I spoke to him, he was absent-minded and didn't reply.
He was listening to the teacher's talk with his mind elsewhere.
I became absent-minded thinking about my girlfriend.
My mother answered distractedly, her mind elsewhere.