Quilt Binding goes around the outer edge of the quilt. It is a long strip of fabric that is sometimes cut on the bias. Not all quilts have binding. Quilts that have binding will last longer (or at least the edges will) than quilts without binding. See our Free Tutorial on Creating and Applying the Binding to the Quilt.
This photo shows samples of binding before being applied to the quilt. You can purchase quilt binding or make your own. The width of the binding is based on the size of the project and your personal preferences. The binding on the left has been made from scraps of fabric.
This photo shows completed quilts with binding. (You do not have to bind a quilt; however, the binding will help the quilt to wear better.)