An idiom meaning extremely quick or instantaneous; lightning-fast speed or action.
彼の判断は電光石火で、相手の隙を見逃さなかった。
His decision was lightning-fast; he didn't miss the opponent's opening.
電光石火の速さで対応したおかげで、大きなトラブルにならなかった。
Because we responded at lightning speed, it didn't turn into a major problem.
彼の手さばきは電光石火の如く、目で追えないほどだった。
His handling was like lightning; it was too fast to follow with the eyes.