Polymorphism and inheritance are key concepts in object-oriented programming. Polymorphism allows objects of different types to be treated as a common type and occurs in two forms: compile-time polymorphism through function/operator overloading and runtime polymorphism through method overriding. Inheritance allows a class to acquire properties and behaviors of its parent class and occurs in single inheritance where a class inherits from one parent and multi-level inheritance where a class inherits from a parent that also inherits from another parent.