Currently, the Debug WebUI's Sessions page captures both active sessions and expired sessions. On the top of the page there is a message along the line of:
This text is ambiguous for me. If all non-active sessions are expired sessions, it should explicitly tell the user that. And since an active session becomes an expired session when it breaches the Session Idle Timeout, the second sentence is also somewhat misleading. User has to "deliberately close" both active sessions and expired sessions to close them.