Real numbers encompass many different types of numbers ranging from integers, natural numbers, and negative numbers, to decimals, fractions, transcendental numbers, and many more. Real numbers include all the types of numbers, and their various forms, that are not imaginary numbers. This is a basic definition of real numbers, and the discussion of real numbers can be significantly more complicated mathematically, and won't be discussed in the context of this site.
The set of real numbers is indicated using this symbol: ℝ.
Examples of real numbers include:
The above is just a small sample of the various forms or types of numbers that make up the real numbers.