Discipline Impact Factor: The Library Science definition is:
Discipline Impact Factor (DIF): DIF is similar to the impact factor, which measures the average number of times a paper in given journal is cited, except that the DIF measures the number of times a paper in a journal is cited in core literature of the given discipline (Hirst, 1978). How does one define core journals in a given discipline. "Citation mapping" is used to generate core journals list in a given discipline. Example Environmental Science.