How is inheritance implemented in PHP?

Inheritance in PHP is implemented using the 'extends' keyword. This keyword is crucial because it establishes a relationship between a parent class (also called a base class or superclass) and a child class (derived class or subclass). When a class extends another class, it inherits all the public and protected properties and methods of the parent class, which promotes code reuse and allows for a hierarchical classification of classes.

Using the 'extends' keyword allows the child class to add its own properties and methods or override the inherited methods from the parent class. This feature of inheritance supports the principles of object-oriented programming, such as polymorphism and encapsulation, making it an essential aspect of PHP development.

In contrast, other terms like 'class' and 'inherits' are not relevant when specifically discussing inheritance. The 'class' keyword is used to define a class itself but does not facilitate inheritance. Similarly, 'inherits' is not a recognized keyword in PHP, thus cannot be utilized to express inheritance. The 'implements' keyword is used in the context of interfaces, allowing a class to implement an interface, which is distinct from the concept of inheritance.