What does the error message "Fatal error: Call to undefined function mysql_connect()" indicate in PHP?

The error message "Fatal error: Call to undefined function mysql_connect()" indicates that the MySQL extension is not enabled in your PHP configuration. This extension has been deprecated since PHP 5.5.0 and removed in PHP 7.0.0. To fix this issue, you need to switch to either MySQLi or PDO extension for connecting to MySQL databases.

// Example of connecting to MySQL database using MySQLi
$servername = "localhost";
$username = "username";
$password = "password";
$database = "dbname";

// Create connection
$conn = new mysqli($servername, $username, $password, $database);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}
echo "Connected successfully";