The Digital Analytics Association, in conjunction with SMMStandards, has proposed definitions for the terms "item," "mention," "reach," and "impressions." You can view and post your comments on these definitions at the #SMMStandards site. Here's a quick summary:
-- ITEM: An ITEM of content is a post, micro-post, article, or other instance appearing for the first time in a digital media.
Comments: This definition of ITEM replaces “clip” “post” and other unclear terminology. ITEMs of content refer to the content vehicle in its entirety, which means that a single ITEM can contain multiple MENTIONs and derivatives. Derivatives of ITEMs such as comments, likes, etc., should not be counted as additional ITEMs.
-- MENTION: A MENTION refers to a brand, organization, campaign, or entity that is being measured.
Comments: MENTIONs are typically defined in Social Media using Boolean search queries. These queries may include AND as well as OR statements to capture specific brand, campaign, or subject matter topics, as they pertain to the goals of the search objective. Further, MENTION queries may also include NOT statements to filter off-topic MENTIONs from the data set.
-- REACH: REACH represents the total number of unique people who had an opportunity to see an ITEM or a valid reproduction of that ITEM across any digital media.
Comments: REACH is typically quantified using social media monitoring tools, social platforms and/or panel based measurement solutions. Each tool, platform, and solution may have a unique method of calculating REACH. For this reason it’s critical to use the Transparancy and Methods table to identify data collection sources.
-- IMPRESSIONS: IMPRESSIONS represent the number of times an ITEM was displayed.
Comments: IMPRESSIONS represent the gross number of items that could have been seen by all people, including repeats. The term “displayed” applies across channels, browsers, devices, and other methods by which an individual might see an item.