What does 'vulnerable' mean?

Question

Uncle Pete is teaching me and my mate Tim to play bridge. He has won every time so far and I am losing loads of money (over £2,000 so far).

Last week on one hand, he played the Ace of Spades three times. Each time he retrieved it from the winning trick to play again. When I tried to do the same next hand he said it was illegal. He was allowed because he was North and Vulnerable.

So how does vulvnerable work? I want to impress him by getting it right next time.

Answer 1

http://www.thefreedictionary.com/

Answer 2

Your uncle is cheating.

At bridge you are not allowed to pick up a card once you have played it.

Don't play cards for money if you don't know the rules.

Answer 3

It usually means easy to get hurt or easily exposed to something.  

here's a dictionary definition:

1. capable of or susceptible to being wounded or hurt, as by a weapon: a vulnerable part of the body.

2. open to moral attack, criticism, temptation, etc.: an argument vulnerable to refutation; He is vulnerable to bribery.

3. (of a place) open to assault; difficult to defend: a vulnerable bridge.