\begin{tabular}{l} Abstract classes do not necessarily have: \\ A0 pointer in their vtable \\ Zero instances of their class \\ Zero references to their class. \\ A virtual function prototype with the notation = \\ 0. \\ \hline\end{tabular}

Abstract classes have a rich history in the world of programming, emerging from the need for better structure and design in object-oriented programming. They allow developers to define a base class that cannot be instantiated, serving as a template for derived subclasses. This concept is vital for implementing polymorphism, where a single interface can represent different underlying forms. In practical programming, abstract classes are incredibly useful when building frameworks or libraries. They enable developers to create a common interface for multiple subclasses while enforcing a contract that these subclasses must adhere to. For example, when designing a game, you might have an abstract class called "Character" with methods like `attack()` and `defend()`, but actual game characters like "Warrior" or "Mage" implement these methods in their unique ways. This keeps your codebase organized and allows for easier maintenance and scalability.