실효성이 · 실효성을
actual effectiveness, practical effect
Example
전문가들은 그 정책의 실효성을 의심하고 있어요.
Experts doubt how effective the policy will actually be.
Word parts
실 real+효 effect+성 quality
Literally 'real effect quality' — does it work in practice, not just on paper?
Good to know
A news favorite: 실효성 있는 대책 'measures that actually work', 실효성이 떨어지다 'to lack real effect'.