an action that is done to prevent something unpleasant or dangerous happening

Many people have been stockpiling food as a precaution against shortages. 为了预防食物短缺，很多人一直在大量储备食品。

They failed to take the necessary precautions to avoid infection. 他们未能采取必要的预防措施来避免感染。

a polite way of referring to contraception (= methods that prevent a woman becoming pregnant)

If you're going to have sex, make sure you take precautions. 发生性行为一定要采取避孕措施。