An impact factor is a quantitative measure of the importance of a journal, article, or researcher (author) relative to others in the same discipline, based on how frequently it is cited. There are several indexes that measure impact factors, but they do not use the same methodologies. This means they produce slightly different results. Therefore, you should use these data carefully. There are some controversial aspects of using impact factors:
All of the information on this page is adapted from University of Washington Health Sciences Library guide on impact factors: https://guides.lib.uw.edu/hsl/impactfactors