what does being volnerable mean?

Someone who is vulnerable is weak and without protection, with the result that they are easily hurt physically and emotionally

If someone is vulnerable to a particular illness they are more likely to get it than other people.

If someone is vulnerable to doing something wrong, they are easily influenced to do it because they are weak, innocent, or in a difficult position.

Something such as a company or a country that is vulnerable is weak, especially financially and economically, and therefore likely to fail.

When a country or place is vulnerable, it is not very well defended and is therefore an easy target to attack.

indefensible [not with an "a"]

capable of being wounded

it means you can be taken advantage of