by A mockbuster (sometimes also called a knockbuster) is a film created with the apparent intention of piggy-backing on the publicity of a major film with a similar title or theme and are often made with a low budget. Often these films are created to be released direct-to-video at the same time as the mainstream film reaches theaters or video outlets. Though the words are often used interchangeably, the term mockbuster implies a spoof or parody of the original film's premise, while knockbuster implies a more derivative (or knock-off) use of a successful film in the same genre.
Though it is possible to use properties of this sort to intentionally deceive consumers into mistakenly purchasing the derivative title (e.g., customer thinks he or she is buying Transformers, but is actually getting Transmorphers), another possible intention[1] is to provide legitimate add-on buying opportunity in the marketplace (e.g., customer enjoyed Will Ferrell's Land of the Lost and wants more in the same sub-genre, and buys/rents C. Thomas Howell's The Land That Time Forgot).
Source: Wikipedia, Mockbuster
