The document discusses the classification of numbers in the real number system. It describes rational numbers as numbers that can be written as fractions with integer numerators and non-zero denominators, including integers. Rational numbers can be expressed with terminating or repeating decimals. Irrational numbers cannot be expressed as fractions and their decimal representations do not terminate or repeat. The real number system consists of both rational numbers, such as integers and numbers with terminating or repeating decimals, and irrational numbers like π.