A session in Drupal is a period of time in which a user interacts with the website. It is a way of tracking a user's activity on the website, and is used to store information about the user's preferences and settings. Sessions are created when a user logs in to the website, and are destroyed when the user logs out or when the session expires.

In Drupal, sessions are stored in the database and are identified by a unique session ID. This session ID is stored in a cookie on the user's computer, and is used to identify the user when they return to the website. The session ID is also used to store information about the user's preferences and settings, such as language, theme, and other settings.

Sessions are important for providing a secure and personalized experience for users. They allow the website to remember the user's preferences and settings, and to provide a more tailored experience. They also help to protect the website from malicious users, as they can be used to track user activity and detect suspicious behavior.

In Drupal, sessions are managed by the Session Manager module. This module provides a secure and reliable way to store and manage user sessions. It also provides a way to set the length of time a session will remain active, and to set the maximum number of sessions that can be active at any one time.