The User engagement metric shows the time that your app screen was in the foreground or your web page was in focus. When your site or app is running but no page or screen is displayed, Analytics doesn't collect the metric. The metric can help you understand when users actively use your website or app.
The metric comes from the user_engagement event. Analytics sends the event when a user navigates off the page, which happens when a user closes their tab or window or when they navigate to another page or screen. The event includes the session engagement status and user engagement duration. The event isn't sent when an event was already sent less than 1 second before the event would have occurred.
Analytics passes the
user_engagement event through the
&_et parameter with every event. Analytics omits the parameter if there was no engaged time since the previous event in the session. For example, Analytics omits the parameter when sending the first_visit and session_start events because no engagement happens before these events. Also, the first event from each page (e.g., page_view) doesn't have an engaged time.