The default keyword in a PHP switch statement is optional.

The default keyword in a PHP switch statement is optional. It serves as the default option when none of the case conditions evaluate to true. The default case is placed at the end of the switch statement and is executed if none of the case values match the expression. However, it is not mandatory to include a default case in every switch statement. If no default case is provided, and none of the case conditions match the expression, the switch statement will simply end without executing any additional code. Including a default case allows you to define a fallback action when no specific cases are met. Learn more: https://www.php.net/manual/en/control-structures.switch.php