Abstraction is the idea of removing levels of complexity. For example, when you press a key on your keyboard and a letter appears on the screen, you don’t need to know how the keyboard interfaces with the computer, or how that stroke is eventually turned into coloured pixels on a screen. That degree of complexity has been abstracted away.
Another example is a calculator. You type in the numbers and decide what you want to do, and your general goal (say, adding two numbers together) is translated into the practicality of performing that action. Your general goal is translated into lots of little more specific ones.
7.1.2 Abstraction in R
The idea of abstraction is a very prevalent one in computer science. R itself is an abstraction; it lets you interface with the CPU without having to know everything about it. And because R is a functional programming language, abstraction is an important thing to understand to write the best possible code.