Fusible Webs refer to a product that is made of a fiber that melts when heated. When it is sandwiched (and melted) between two pieces of fabric, it will fuse the two fabrics together. Adhesives cover a range of products that stick on to a fabric one way or another. They can be used to close seams, to mend holes, to add a finish to or fuse things together. My current favorite example of an Adhesive is Pellon's Vinyl Fuse. Iron-on vinyl adds a clear, protective layer to fabrics. Most interfacing is fused to the wrong side of the fabric. However, this product is fused to the right side so it provides a cosmetic embellishment in addition to extra support. It gives your fabric the look of vinyl and adds a water repellent and UV rated upgrade.