Lowering a 95 Accord

I am looking to get a set of springs to lower my car.

http://www.procarparts.com/store/di...-XXGL-0103-GLSX

But the manufacturer is saying that I have to "Trim the bump stop"

What is a "Bump Stop"

If I bought a better pair of springs, would I still have to do this? Or is this something you have to do with all lowering kits.

www.importzrus.com