There is no authoritative definition of the term "patent grant-back." It has been defined as a clause in a patent license which provides "for license or assignment to the licensor of any improvement patented by the licensee in the products or processes of the licensed patent." In litigated cases grant-back clauses usually appear either in basic patent licenses or in licenses of the products or processes of an industry which the licensor dominates through control of a multitude of overlapping patents.
Eric E. Bergsten S.Ed.,
Patents - Licensing - Legality of Grant-Back Clauses,
Mich. L. Rev.
Available at: https://repository.law.umich.edu/mlr/vol55/iss5/5