What is this bracket?

[Baby John]

I've been meaning to ask this question but seeing the picture in another thread reminded me. On my sons truck we have a bracket on one side of the frame in the rear but there's not a matching bracket on the other side. So what is this for?

Look at the attached picture and you'll see what I'm talking about. It's a little steel bracket that's on the side of the frame, just in front of the driver's side rear tire.

Edit: Well, looking at the picture now I can tell that this particular bracket sits above the axle with a bushing on it so I think I know what this particular bracket is. Maybe this picture doesn't show what I'm talking about. Let me look and see if I can find a picture of our truck.