According to Wikipedia:
"Altmetrics are new metrics proposed as an alternative to the widely used journal impact factor and personal citation indices like the h-index. The term altmetrics was proposed in 2010, as a generalization of article level metrics and has its roots in the twitter #altmetrics hashtag. Although altmetrics are often thought of as metrics about articles, they can be applied to people, journals, books, data sets, presentations, videos, source code repositories, web pages, etc. Altmetrics cover not just citation counts, but also other aspects of the impact of a work, such as how many data and knowledge bases refer to it, article views, downloads, or mentions in social media and news media."
Adie, E. and Roe, W. (2013), "Altmetric: enriching scholarly content with article-level discussion and metrics." Learned Publishing, Vol. 26 No. 1, pp. 11-17.
Mas-Bleda, A., Thelwall, M., Kousha, K. and Aguillo, I.F.(2014), "Do highly cited researchers successfully use the social web?" Scientometrics, Vol. 101 No.1, pp337-356.
Priem, J., Taraborelli, D., Groth, P. and Neylon, C. (2010), "Altmetrics: a manifesto", available at http://altmetrics. org
Shuai, X., Pepe, A. and Bollen, J. (2012), "How the scientific community reacts to newly submitted preprints: article downloads, Twitter mentions, and citations", Plos One, Vol. 7 No. 11.
SPARC primer on ALMs http://www.sparc.arl.org/initiatives/article-level-metrics
Sud, P. and Thelwall, M. (2014), "Evaluating altmetrics", Scientometrics, Vol. 98 No. 2 pp.1131-1143.
Zahedi, Z., Costa, R. and Wouters, P. (2014a), "How well developed are altmetrics? A cross-disciplinary analysis of the presence of 'alternative metrics' in scientific publications" Scientometrics Vol. 101 No. 2, pp. 1491-1513.
Presentation: Beyond traditional impact: What can Altmetrics do for you? http://lgdata.s3-website-us-east-1.amazonaws.com/docs/999/964800/Oxford_-_Altmetric_com.pdf