Session tracking allows servers to maintain state for individual users across multiple requests or page visits. The HttpSession interface provides a way to do this in Java web applications. It acts as a hashtable associated with each user, allowing information to be stored and retrieved by key. Developers can store data in a session using setAttribute, retrieve it with getAttribute, and remove it with removeAttribute or by invalidating the entire session. Some servers support distributed and persistent sessions to allow session data to be accessed across multiple servers for load balancing or survive server restarts.