expression, i-adjective
Describes someone who thinks fast, grasps things quickly, or is mentally agile. Often used as a compliment.
See also: 頭の回転 (あたまのかいてん)
彼は頭の回転が速いから、どんな質問にもすぐ答えられる。
He's quick-witted, so he can answer any question right away.
頭の回転が速い人は、会話のテンポがいい。
People who are sharp have a good conversational rhythm.