In computer science, abstraction refers to removing unnecessary attributes and data fro objects or systems in order to focus attention on crucial details. The process can be compared to generalizing something - the more broad and concise something is, the easier it is to understand its function! Abstraction is fundamental to object oriented programming and computer science in general.
Abstractions may also refer to real-world objects and systems, rules of computational systems or rules of programming languages that carry or utilize features of abstraction itself, such as:
the usage of data types to perform data abstraction to separate usage from working representations of data structures within programs; the concept of procedures, functions, or subroutines which represent a specific of implementing control flow in programs; the rules commonly named "abstraction" that generalize expressions using free and bound variables in the various versions of lambda calculus; the usage of S-expressions as an abstraction of data structures and programs in the Lisp programming language; the process of reorganizing common behavior from non-abstract classes into "abstract classes" using inheritance to abstract over sub-classes as seen in the object-oriented C++ and Java programming languages.