a film in which the technical style of a documentary is applied to a fictional subject, or, sometimes, to the dramatization of the story of a real person or situation, so as to add authenticity and realism
See semidocumentary in American Heritage Dictionary 4
nounpl.sem·i·doc·u·men·ta·ries
A book, movie, or television program presenting a fictional story that incorporates many factual details or actual events.