Abstraction is one of the 4 main OOP principles.
The objective is to present only the necessary information to the user. The unnecessary details remain hidden.
Example:
Result:
In this example the person who uses the class is only concerned about the area of the triangle.
The one who uses the class doesn't care about the way an area is calculated. The important information is the calculated area. The details that remain hidden are the calculations for the area.