I don’t just call sessions a metric, but rather, a ‘meta metric,’ because a session can encompass other metrics. For example, pageviews is a metric, and within a single session, there can be many, many pageviews.
Anyway, yesterday, Google’s Analytics channel had a tweet about this topic.
The tweet linked to an article on the Semrush blog, titled, Sessions in Google Analytics: What You Need to Know & How to Use the Data. This article is by Connor Lahey, and describes various aspects of the sessions metric. It gave a good definition of sessions, talked about its significance, and how to set it up.
Perhaps the most distinguishing content in this article is how to use Analytics and Semrush together. You basically connect the 2 tools together, and you get more insight.
Source: Google Analytics Twitter channel