Inheritance is a fundamental concept in object-oriented programming where a new class is created by inheriting properties and behaviors from an existing class. The new class, known as the derived class or subclass, can reuse and extend the functionalities of the base class or superclass.

Inheritance allows for code reuse, as common properties and behaviors can be defined in a base class and inherited by multiple subclasses. It also promotes modularity and extensibility, as subclasses can add or modify the inherited behaviors to suit their specific requirements.

Inheritance is achieved through the use of inheritance keywords or modifiers like “extends” (Java) or “inherits” (C++). When a subclass inherits from a superclass, it gains access to all the public and protected properties and methods of the superclass. The subclass can then override or extend these inherited members as needed.

Single inheritance allows a class to inherit from only one superclass, whereas multiple inheritance allows a class to inherit from multiple superclasses. Single inheritance is simpler and less prone to conflicts, but multiple inheritance can provide more flexibility and code reuse in certain scenarios.

The diamond problem is a scenario that occurs in multiple inheritance when a class inherits from two or more superclasses that have a common superclass. It leads to ambiguity when the subclass tries to access a member that is inherited from the common superclass. To resolve this, programming languages provide mechanisms like virtual inheritance or interface implementation to explicitly resolve the ambiguity.