An impact factor is, broadly speaking, a measurement of the "the average number of times recent articles in a specific journal were cited in a particular year".
For example: The impact factor for 2003 was based on citations made in 2003 to articles published 2001 and 2002.
Click Impact factors for all of the Nature Publishing Group Journals.
If you would like additional information about impact factors, please visit https://clarivate.com.