Typosquatting is the profiting, through adverts, from websites whose addresses are very close to famous brand names. A typical site could be microsift.com. When visitors go to a typosquatter's site they see adverts which, when displayed, pay the site operator a small fee.
Though the money earned by each advert is often only a few dollar cents, the volume of traffic and the number of domains held by professional typosquatters means that some are earning millions of dollars a year.