title: What, logically and physically, is a session?
body: <p>This is a quite basic question about some concept.</p>
  
  <p>What's the definition of a session in the context of a Web server, such as IIS or Apache. What is a session both physically and logically?</p>
  
  <p>How to determine a session is <strong>started</strong> or <strong>ended</strong>? Use a <strong><em>server-side</em></strong> timer or something?</p>