A session on a website or app represents the set of actions, such as visited pages, events, or e-commerce transactions, done by a visitor within a specific time-range.
A session represents a set of visitor interactions with a website or app within a given time range.
The visitor interaction of a session can cover the following:
By default, a session lasts 3 hours. This, basically, means when a visitor lands on the site, tracking is started, and all the activity is clustered until the session ends.
After 3 hours, the expiration time resets by adding on an additional 3 hours from the time of that interaction.
Therefore, a single user can open as many sessions as they want (for every visit on the site after more than 3 hours from the last action) - be it in the same day, or over several days, weeks, or months.