Built-In dishwashers are built into the cabinets below the counter. These are very common in North America.
Drawer dishwashers, like traditional units, are built into the cabinets below the counter, but operate very differently; rather than a drop-door, they are installed as a drawer. They are either semi-integrated or fully integrated units.
Portable dishwashers are freely moveable and can be installed anywhere in your home with the proper plumbing.
Countertop dishwashers are small enough to fit right on top of any surface in your kitchen. They are meant to handle smaller loads like utensils.