I think of the 4-bar as having links that are parallel throughout the travel of the suspension. Maybe that is better known as a parallel 4-bar. The 4-link is a more sophisticated system in which the bars are not parallel and have multiple mounting points at the axle and the frame. I don't know how to describe the triangulated 4-bar but I think it is similar to what is used on mustangs and GM unibody cars. Go to this site, "http://www.artmorrison.com/index.html", under rear suspension there will be pictures of all three types.