The idea behind OOP is that computer systems modeled after the real-world environment that they represent are more adaptable. What does this really mean? Well, each phrase taken independently is self-explanatory. Hopefully, the concepts of "computer systems," "real-world environment," and "adaptability" are easily understood , but what about the concept of "modeling"? This simply refers to how a computer system is designed. Thus, a computer system modeled on real-world entities refers to an application that is comprised of units with characteristics and behaviors similar to their real-world complements.
An example here might help. Imagine a human resources (HR) department. In that department, an HR employee is responsible for dealing with employees , jobs, benefits, and salaries. Therefore, an object-oriented system to support this HR department will have entities (known as objects) such as Employee , Job , and Benefit . The closer the characteristics and behaviors of an Employee entity in the system resemble those of a true employee, the easier it is to adapt the system to changes in the business.