A hardshell is a fully waterproof jacket, and is usually breathable, as well. When I say fully waterproof, I mean that the jacket itself is made with a waterproof fabric, and that the seams of the garment are full sealed, or welded, for absolute waterproof integrity. Some companies, in order to cut costs, may only seal the critical seams, like those on the hood, shoulders and arms. Others might make a waterproof jacket that features waterproof fabric, but does not have sealed seams. The checklists on review pages will indicate whether a garment is seam sealed or not. If you want absolute protection from the elements, you should look into buying a hardshell.