Final answer:
Inheritance is the Object-Oriented Programming concept designed as a reuse mechanism, allowing new classes to inherit attributes and methods from existing ones and promoting code reuse.
Step-by-step explanation:
The Object-Oriented Programming (OOP) concept used as a reuse mechanism is inheritance. Inheritance allows a new class, known as a subclass, to inherit attributes and methods from an existing class, referred to as a superclass. This concept enables developers to create a new class with existing functionality, thereby promoting code reuse.
Polymorphism is another OOP concept, which allows objects to be treated as instances of their parent class rather than their actual class. Encapsulation is the bundling of data with the methods that operate on that data, and abstraction is the concept of hiding the complex reality while exposing only the necessary parts. While all of these are key OOP concepts, inheritance is specifically designed for reuse.