In PHP, you can define an interface using the interface keyword like interface InterfaceName { ______ }.

In PHP, to define an interface, you can indeed use the interface keyword followed by the name of the interface. For example: interface InterfaceName { } An interface contains method signatures without implementation and can also define constants. Interfaces establish a contract that classes must adhere to when implementing the interface. Classes that implement an interface must provide an implementation for all the methods defined in the interface. To learn more about interfaces in PHP, refer to: http://php.net/manual/en/language.oop5.interfaces.php