Like having a session with a professional, that is, you visit a professional for a continuous hour, then perhaps visit again every month for another session. Likewise, a user comes to your web site and has a session to complete a particular task.
For the purposes of ConversionRuler, a Session is any interaction where time between clicks or page loads is no longer than 30 minutes.
After 30 minutes, the web site visitor's interaction is considered another session. This only occurs if the time between the last page view and the current page view is more than 30 minutes; it is not based on the first page view on the site, rather the last interaction with the site.
Sessions make a little more sense when discussed relative to users. A user is an individual who visits a web site over time, with multiple Sessions. In short, it is a single computer and browser (usually meaning a single person) who visits your site for one or more sessions.
Session cookies expire after a half an hour, and are reset to expire every page view (or action).
User cookies never expire.