Impact factor (IF) of an academic journal is a measure reflecting the average number of citations to recent articles published in that journal. It is frequently used as a proxy for the relative importance of a journal within its field, with journals with higher impact factors deemed to be more important than those with lower ones. The impact factor was devised by Eugene Garfield, the founder of the Institute for Scientific Information. Impact factors are calculated yearly starting from 1975 for those journals that are indexed in the Journal Citation Reports.
It is a measure of the frequency with which the average article in a journal has been cited in a particular year. If you’d like to publish your academic paper in a prestigious journal, you need to pay attention the the impact factor of the journal you’d like to submit your manuscript to.