preventive measure; prevention measure
A plan, policy, or concrete step taken to stop something undesirable from happening.
Hand washing is recommended as a preventive measure against infectious diseases.
We will consider measures to prevent the accident from happening again.
対策 is a broader term for countermeasures or steps to deal with a situation, not necessarily limited to prevention.
Compound of 防止 (prevention) + 策 (plan, measure).