A journal’s impact factor is determined by the average number of citations received in a year by articles published in the journal in the previous two years. If a journal has an impact factor of 2 in 2015, it means that on average papers in this journal received 2 citations in 2014, 2013. It is used as an indicator of quality as a journal with a high impact factor is considered better than those with a low impact factor. The impact factor is used to compare different journals within a certain field. However, its use is not without controversy and it should be taken as an indication only. This video provides a short overview of how the JCR should be used.
Journal Citation Reports (JCR)
This is a database that allows the user to identify the impact factor of a particular journal. Initially the user must choose between the Sciences or the Social Sciences and then select by Subject Category, Publisher or Country/Territory. Entering the name of the journal into the search box brings up the journal’s details. This video provides a short overview of how to use the JCR.
There are other free sources of information in this area