A class is a definition of the properties and methods of a particular type of object. When a class is used to define a new object, the resultant object is referred to as an instance of that class. In a PHP class definition, properties are variables, methods are functions.

Type System ¶ PHP uses a nominal type system with a strong behavioral subtyping relation. The subtyping relation is checked at compile time whereas the verification of types is dynamically checked at run time. PHP's type system supports various atomic types that can be composed together to create more complex types.

PHP does not require explicit type definition in variable declaration. In this case, the type of a variable is determined by the value it stores. That is to say, if a string is assigned to variable $var , then $var is of type string. If afterwards an int value is assigned to $var , it will be of type int.

To create an object in PHP, you use the 'new' keyword followed by the class name. This will create an instance of the class which can then be used to call any public methods or access any public properties defined within the class. This is crucial in OOP as it allows for code reusability and modularity.