The term was originally coined in Altmetrics: A manifesto, (J. Priem, D. Taraborelli, P. Groth, C. Neylon, 2010). The manifesto and hashtag were the first use of the specific term "altmetrics," following the 2008-09 discussion among academics about how to track impact from online usage and discussion of scholarly articles.
These tools are both projects of the nonprofit OurResearch, originally co-founded by open advocates Jason Priem and Heather Piwowar
The major commercial altmetric tools, Plum Analytics and Altmetric, are most commonly used through integration with other products.
PlumX metrics include policy citations, news mentions, Wikipedia citations, and social media usage including likes, shares and recommendations.
Stevens has access to Plum through Scopus and ScienceDirect, and you may also come across PlumX metrics in some open access journals.
Altmetric is often used by institutions and publishers to show research impact. Individual researchers may also make use of the Altmetric dashboard or a free badge to put on a CV or resume.