What's It Mean to Trust?

If I trust you, what does that mean? What does it mean for you to trust me? Here's a great definition of trust from The Five Dysfunctions of a Team:

• Trust is the confidence among team members that their peers' intentions are good and that there is no reason to be protective or careful around the group. In essence, team members must get comfortable being vulnerable around each other.

I trust you when I don't have to be protective or careful around you. I trust you when I know you're looking out for me--even when I'm not in the room.