Real Number System
You can divide the real numbers into two major groups: Rational & Irrational.
Irrational numbers are numbers that can be made into a decimal that goes on forever, but it does not repeat or terminate(end). For example, an irrational number can look like this 3.56469882224689....
All other real numbers are classified as rational.
Rational numbers can be subgrouped into natural numbers, whole numbers, and integers.
Natural numbers are the counting numbers. 1,2,3,....
Whole numbers are natural numbers plus zero. 0,1,2,3...
Integers are whole numbers plus their opposites. ...,-2,-1,0,1,2,...
All of those subgroups are rational numbers, but rational numbers can be decimals too (as long as they repeat or terminate). For example, some rational numbers are 3.45498, 2.3333333..., 8.5
Here is a chart that may help you visualize classifying real numbers:
