Ruching is a term for gathering in order to create style in your garments.  You can ruche by creating gathering stitches or ruche by utilizing elastic.  This demonstration covers the latter.  I show you how to easily recreate this detail in my example of creating a sleeve with ruching.  This technique is something you'll be able to easily replicate and yet your friends will be amazed at your new found talent.  Because ruching will shrink an area as it gathers, make sure that the piece you are ruching has extra length to accommodate it.