Typosquatting is the practise of registering domain names matching frequent typos made when accessing well known websites.
When a user types in the matching typo in a browser address bar, it produces a visit. The visit is then monetized through different means (affiliate programs, domain parking, sponsored links, MFA, etc..).
When the typosquatting targets a merchant site, the more profitable monetization method is affiliate program with this merchant before being discovered.
The potential revenues associated with typosquatting is declining because web users are using less and less browser address bars for the benefit of search engine search boxes.
Another reason for the potential decline is lawsuit risks for typosquattters.. There is now well-established case law in this field and big brands fight back typosquatters.
Some large traffic websites may be or have been confronted with several hundreds of typo domains.
Some examples of current or ex typos for 2 web heavyweights: