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Inheritance is a mechanism in Object-Oriented Programming that allows a class to inherit the properties (instance variables) and methods (functions) of another class. This helps create a parent-child relationship between the two classes, where the parent class is known as the superclass and the child class is called the subclass. Inheritance helps in code reusability, as the subclass can utilize the functionality of its superclass without having to rewrite the same code.

A subclass inherits the following from its superclass: 1. Instance variables: A subclass can inherit and access the instance variables (also known as attributes) of its superclass. These variables can be used to store data related to individual instances of the class. 2. Methods: A subclass can inherit and use the methods (functions) defined in its superclass. These methods represent the actions that can be performed by objects of the subclass. 3. Constructors (implicitly): Subclasses do not inherit superclass constructors directly, but a subclass must call a constructor of its superclass before proceeding with its own initialization. This ensures that the superclass portion of the subclass object is correctly initialized. 4. Inner classes and interfaces: A subclass can inherit inner classes and interfaces defined within the superclass by calling them through super keyword.

The inheritance of instance variables and methods depends on the visibility modifiers used to define them in the superclass. There are three main visibility modifiers: 1. Public: An instance variable or method declared as public in the superclass is accessible to the subclass and can be inherited without any restriction. 2. Private: If an instance variable or method is declared as private in the superclass, it cannot be accessed or inherited by the subclass. 3. Protected: An instance variable or method declared as protected in the superclass is accessible to the subclass within the same package and can be inherited by subclasses in different packages as well.

A subclass can provide a new implementation for a method inherited from its superclass. This is called method overriding. When a subclass overrides an inherited method, the method in the subclass with the same signature (name and arguments) replaces the method inherited from its superclass. This allows the subclass to customize or enhance the method implementation according to its specific requirements. In conclusion, a subclass inherits the instance variables, methods, constructors (indirectly), and inner classes and interfaces of its superclass, depending on the visibility modifiers used in the superclass. They can access and use this inherited functionality to build upon and extend the features of the superclass.