The PHP include_once keyword is used to embed PHP code from another file. If the file is not found, a warning is shown and the program continues to run.

The PHP instanceof keyword is used to check if an object belongs to a class, and returns true if the object is an instance of the class or false if not.

The PHP insteadof keyword allows you to select from which trait a method should be taken if more than one trait has a method with the same name.

The PHP interface keyword is used to create interfaces, which is a structure which defines a list of methods that must exist in a class.

The PHP namespace keyword is used to declare in which namespace a PHP file is operating.

The PHP new keyword is used to create an object from a class.

The PHP print keyword is used to output text. Unlike echo, print can only output one string at a time.

The PHP private keyword is an access modifier that marks a property or method as private.

The PHP protected keyword is an access modifier. It marks a property or method as protected.

The PHP public keyword is an access modifier, and marks a property or method as public (meaning it can be used by any code that can access the object).

The PHP require keyword is used to embed PHP code from another file. If the file is not found, a fatal error is thrown and the program stops.

The PHP require_once keyword is used to embed PHP code from another file.

The PHP return keyword ends a function and uses the result of an expression as the return value of the function.

The PHP static keyword is used to declare properties and methods of a class as static (can be used without creating an instance of the class).

The PHP throw keyword is used to throw exceptions to change the program flow if an unexpected situation arises, such as invalid data.

The PHP trait keyword is used to create traits, which are a way to allow classes to inherit multiple behaviors.

The PHP try keyword is used to create a try…catch, or a try…catch…finally statement.

The PHP use keyword tells a class to inherit a trait and it gives an alias to a namespace.