What does $R$ mean in math?

Real numbers:

In mathematics, the alphabet $R$denotes the set of real numbers.

The real numbers are classified as:

1. Rational numbers: These numbers can be written as a ratio of two integers numbers, provided, a non-zero denominator.$Q=\frac{1}{2},\frac{4}{5}...$
2. Integer: These are negative, zero, or positive whole numbers that do not include fractions. $I=\left\{....-3,-2,-1,0,1,2,3,4...\right\}$
3. Whole numbers: These are positive whole numbers including zero. $W=\left\{0,1,2,3,4...\right\}$
4. Natural numbers: These are positive whole numbers. $N=\left\{1,2,3,4...\right\}$
5. Irrational numbers: These numbers cannot be written as a ratio of two integers numbers.For example $\sqrt{2},e,\mathrm{\pi }....$

Hence, the meaning of $R$ is explained.