Me personally, I define trust as in what I will allow myself to do with/around another person, or what I will allow another person to do with/around me. I'm not sure if this makes sense though. An example would be an ex of mine who asked me to marry him; well, for one I never trusted him. We weren't together long enough for me to trust him. He asked me three times, and each time I said no, that I didn't trust it; that relationship didn't last much longer.
Talking about myself...there are quite a few things about my life that I honestly don't mind talking about. I will gladly talk to people about my family, past, present, etc., if they ask. It's when we start getting into emotional, or very personal talking, that I don't feel right talking to just anyone about it.