1. （人或地方）未受保护的，未设防的
An unprotected person or place is not looked after or defended, and so they may be harmed or attacked.

2. 暴露在外的；易受损的
If something is unprotected, it is not covered or treated with anything, and so it may easily be damaged.

3. 未用避孕套的；无防护的
If two people have unprotected sex, they do not use a condom when they have sex.

1. lacking protection or defense