Define the Abstraction of OOA

Now, let us see how objects can be seen as a problem, and find their associated data and their behaviour. You will notice that an object is an abstraction, or real life entity. 

In our day life we deal with complexity by abstracting details away. 

Let us see this with an illustration of: Driving a car never requires knowledge of internal combustion engine. It is enough to think of a car as simple transport. 

In easy term, abstraction means to focus on the crucial, inherent aspects of an entity, by avoiding its accidental properties. Abstraction is a usual process that we do every day. When you view the world, it is impossible to take in every minute detail, so you only concentrate on the aspects that are more important.

An abstraction is an easy overview of a system that captures the necessary elements of that system (from the outlook of the needs of the modeller), while suppressing all other elements.