Bibliometrics refers to measuring impact by counting citations, specifically by counting how many times a particular work has been cited by other works.
Video: "How to Use Bibliometrics Effectively," from Web of Science
Priem, J., Piwowar, H.A., & Hemminger, B.M. (2013). Altmetrics in the wild: Using social media to explore scholarly impact. Pre-print. Retrieved from http://arxiv.org/abs/1203.4745v1.