Forbes.com:

The Web is like an iceberg divided into three segments, each with its own cluster of hangouts for cyber criminals and their digital breadcrumbs. The tip of the iceberg is the “Clear Web” (also called the Surface Web), indexed by Google and other search engines. The very large body of the iceberg, submerged under the virtual water, is the “Deep Web”—anything on the Web that’s not accessible to the search engines (e.g., your bank account). Within the Deep Web lies the “Dark Web,” a region of the iceberg that is difficult to access and can be reached only via specialized networks.