In PHP, sessions are a mechanism for storing user-specific data across multiple web pages. Sessions are started using the PHP `session_start()` function. Once a session is started, a unique session ID is generated and stored on the user’s computer. This session ID is used to identify the user and their session data on subsequent requests.
There are several ways to check if a session has already been started in PHP. One way is to use the PHP `session_status()` function. The `session_status()` function returns an integer value that indicates the current status of the session. The possible values are: