Traits are a mechanism for code reuse in single inheritance languages such as PHP. A Trait is intended to reduce some limitations of single inheritance by enabling a developer to reuse sets of methods freely in several independent classes living in different class hierarchies. The semantics of the combination of Traits and classes are defined in a way that reduces complexity and avoids the typical problems associated with multiple inheritance and Mixins. A Trait is similar to a class, but only intended to group functionality in a fine-grained and consistent way. It is not possible to instantiate a Trait on its own. It is an addition to traditional inheritance and enables horizontal composition of behaviour; that is, the application of class members without requiring inheritance. sayHello() . " " . $world->sayWorld(); //Hello World