Not all domain names are actively used by their owners. Some domains were registered for speculative reasons, to be sold for a profit later on or are reserved for future projects. Those domain names generally resolve in a blank page when opened in the browser. To avoid, domain owners can forward their unused domain names to specialized domain parking companies, which show advertisements and banners on the domain instead of a white page.
The generated profit from these banners is then shared with the domain owner, allowing them to earn some money from their domain names while they aren’t not in use. Some individuals and companies hold a huge portfolio of domain names, simply to profit from the parking revenues.