i-adjective
cheerfully working; quick to act; light on one's feet
Describes someone who is eager and quick to take action, especially in helping or doing tasks. Often used positively for a person who doesn't hesitate to move or work. Compare with 腰が軽い, which is the dictionary form.
See also: 腰が軽い
彼は腰の軽い人で、何かあるとすぐに手伝ってくれる。
He is a quick-to-act person; whenever something comes up, he helps right away.
腰の軽いスタッフのおかげで、準備が早く終わった。
Thanks to the staff who were quick to pitch in, the preparations finished early.
Idiomatic phrase combining 腰 (waist/hips) and 軽い (light). The imagery suggests someone whose hips are light, implying readiness to stand up and move quickly. The exact origin is uncertain, but it is a common metaphor in Japanese.