A session is a group of user interactions with a website bundled into a single unit, from arrival to departure. For example, if a user visits a site, views 3 pages, and leaves, that counts as one session.
Session boundaries vary by analytics tool. In Google Analytics 4 (GA4), a session ends when: 30 minutes pass without activity (timeout), the date changes (midnight), or the traffic source changes (e.g., arriving via Google search, then returning via a social media link).
Understanding the difference between sessions and pageviews (PV) is important. If one session includes 5 page views, the session count is 1 and PV is 5. The distinction from unique users (UU) also matters: if the same user visits once in the morning and once in the afternoon, UU is 1 but session count is 2.
In short URL click analytics, the session concept is crucial. When the same user clicks a short URL multiple times, raw click count and unique click count differ. To accurately measure marketing effectiveness, compare unique clicks against session data to understand how many actual users reached the destination.
Key session-related metrics include pages per session (engagement depth), average session duration (engagement quality), and bounce rate (single-page sessions). GA4 introduced "engaged sessions" - sessions that last over 10 seconds, include 2+ page views, or trigger a conversion event. Related books are available on Amazon.