To become distracted; to lose concentration because attention is pulled away by something else.
授業中に窓の外の鳥の声で気が散って、先生の話が聞けなかった。
During class I was distracted by the sound of birds outside the window and couldn't follow the teacher's talk.
試験勉強をしているときに携帯が鳴ると気が散るから、電源を切っておいた。
When I'm studying for an exam, a ringing phone distracts me, so I turned it off.
雑音が多いカフェでは仕事に集中しづらくて、すぐに気が散ってしまう。
In a café with a lot of background noise it's hard to concentrate and I quickly get distracted.
小さい子供が近くにいると、どうしても気が散って作業が進まない。
When a small child is nearby I inevitably get distracted and can't make progress on my work.