A Session is a group of actions (eg. link clicks, pageviews, downloads) one user takes within a given time frame on your website. In Capturly, this default time frame is 30 minutes.
Example: Your potential visitor finds an article online. In that article there is an anchor text or Call-To-Action that directs traffic to your website. After clicking on it, you’ll gain a Visitor and his Session will start. The visitor browses more of your content, then stops being active for 30 minutes without closing your website. After 30 minutes – and the first session – expired, the visitor becomes active again (e.g. browses more content, subscribes to newsletter). This will count as a second Session.