• Object
    This is the basic unit of object-oriented programming. That is both data and function that operate on data are bundled as a unit called as object.

  • Class
    When you define a class, you define a blueprint for an object. This doesn’t actually define any data, but it does define what the class name means, that is, define what an object of the class will consist of and what operations can be performed on such an object.

  • Abstraction
    Data abstraction refers to, providing only essential information to the outside world and hiding their background details, i.e., to represent the needed information in program without presenting the details.
    For example, a database system hides certain details of how data is stored and created and maintained. Similar way, C++ classes provides different methods to the outside world without giving internal details about those methods and data.

  • Encapsulation
    Encapsulation is placing the data and the functions that work on that data in the same place. While working with procedural languages, it is not always clear which functions work on which variables but object-oriented programming provides you framework to place the data and the relevant functions together in the same object.

  • Inheritance
    One of the most useful aspects of object-oriented programming is code reusability. As the name suggests Inheritance is the process of forming a new class from an existing class that is from the existing class called as base class, new class is formed called as derived class.
    Code reusability -> Reduce the code size.

  • Polymorphism
    Poly refers to many. The ability to use an operator or function in different ways. In other words, giving different meaning to the operators or functions is called polymorphism. That is a single function or an operator functioning in many ways different upon the usage is called polymorphism.

  • Overloading
    The concept of overloading is also a branch of polymorphism. When the exiting operator or function is made to operate on new data type, it is said to be overloaded.

https://docs.microsoft.com/en-us/windows/desktop/fileio/i-o-completion-ports