When completing an object-oriented design, there are five basic concepts to understand: classes/objects, encapsulation/data hiding, inheritance, polymorphism, and interfaces/methods.

1. Objects are the basic unit of OOPS representing real-life entities. They are invoked with the help of methods. These methods are declared within a class. Usually, a new keyword is used to create an object of a class.
   Class is a predefined or user-defined template from which objects are created. It represents properties/methods that are common to all objects of the same class. It has several features, such as access modifiers, class names, interfaces, and class bodies.
2. Abstraction means showing only the relevant details to the end-user and hiding the irrelevant features that serve as a distraction. For example, during an ATM operation, we only answer a series of questions to process the transaction without any knowledge about what happens in the background between the bank and the ATM.
3. Encapsulation is a means of binding data variables and methods together in a class. Only objects of the class can then be allowed to access these entities. This is known as data hiding and helps in the insulation of data.
4. Inheritance is the process by which one class inherits the functions and properties of another class. The main function of inheritance is the reusability of code. Each subclass only has to define its features. The rest of the features can be derived directly from the parent class.
5. Polymorphism means "many forms", and it occurs when we have many classes that are related to each other by inheritance. Like we specified in the previous chapter; Inheritance lets us inherit attributes and methods from another class. Polymorphism uses those methods to perform different tasks.

OOP (Object-Oriented Programming) concepts are a set of principles that provide a framework for designing and developing software using the object-oriented paradigm. The five major Object-Oriented Concepts are:

• Abstraction: Abstraction is the process of selecting and representing the essential features of an object while ignoring the non-essential details. In OOP, abstraction is achieved through classes and objects, which represent real-world entities and concepts in a simplified manner.
• Encapsulation: Encapsulation is the practice of hiding the internal details of an object from the outside world, and only exposing a public interface that can be used to interact with the object. This protects the object from unwanted external interference and allows for better management of complex software systems.
• Inheritance: Inheritance is a mechanism that allows new classes to be derived from existing classes, inheriting their properties and behaviors. Inheritance facilitates code reuse and allows developers to create hierarchies of related classes that share common attributes and methods.
• Polymorphism: Polymorphism is the ability of an object to take on different forms depending on the context in which it is used. In OOP, polymorphism is achieved through method overriding and overloading, which allow different objects to respond to the same method call in different ways.
• Class and Object: A class is a blueprint for creating objects that define a set of attributes and methods that are common to all instances of the class. An object is an instance of a class that has its own unique set of attribute values and method behaviors.