What is the role and purpose of sessions in the context of web applications or systems?

Sessions in web applications are used to maintain state between requests from the same user. Since HTTP is a stateless protocol, the server does not store user information between requests by default.

Role of sessions:

• User identification over multiple requests.
• Storing user data (e.g., authentication details, settings, cart contents).
• Ensuring personalization and security.

In PHP, sessions are usually implemented through a unique session identifier (session ID), which is stored in the browser's cookie. With each request, the server receives this ID and loads the corresponding session data.

Example of usage in PHP:

session_start(); // starts a session or resumes an existing one
$_SESSION['user_id'] = 123; // storing data in the session
// later, you can retrieve this data
echo $_SESSION['user_id'];

Thus, sessions allow "remembering" the user and their state between requests.