Altmetrics are the metrics applied to the scholarly outputs, usually scholarly journal articles, that demonstrate the attention, such as shares and mentions, on social media, news, public policy, patents, syllabi, YouTube, Reddit, and other "alternative" metrics outside of scholarly citations. Two competing altmetrics data providers provide the majority of this data to researchers, administrators, publishers, and students: Altmetric and Plum Analytics (PlumX). Virginia Tech subscribes to Altmetric's database, Altmetric Explorer. See below for a link to setup an account.
Here's an example of an article with online attention: The Toxic Truth about Sugar (Nature), which has Altmetric attention from news media outlets, blogs, and Twitter users (also see the PlumX details for comparison between the two data sources).