Q. Impact Factor?

What it is:

The impact factor of a journal is a rating for the extent to which the articles in that journal have been cited by other researchers. It's an average of the number of times the articles in a journal have been cited in the previous two years divided by the number of articles in the journal that were citable.

How to find it:

Search Journal Citation Reports

More:

Modified calculations for journal impact using Web of Science data are also freely available online through Eigenfactor Journal Rankings. Modified calculations for journal impact using Scopus data are freely available online through Scimage Journal Rankings. 

N.B:

You should not depend solely on citation data in your journal evaluations. It is not meant to replace informed peer review. Careful attention should be paid to the many conditions that can influence citation rates such as language, journal history and format, publication schedule, and subject specialty.