A rational number can be written as a fraction a/b, where a and b are integers and b is not zero. Examples: 1/2, −3/4, 5 (which is 5/1), and 0.75 (which is 3/4). Every integer is rational. Every terminating or repeating decimal is rational.

The rational numbers are dense: between any two rationals, there is another. Yet they do not fill the number line completely. Irrational numbers like √2 and π occupy the gaps. Together, rational and irrational numbers form the real numbers.

Rational numbers are closed under addition, subtraction, multiplication, and division (except by zero). They form a field, a structure studied in abstract algebra. In everyday life, fractions and decimals are rational numbers, and they handle most practical calculations.

• Can be written as a ratio of integers
• Includes integers and terminating/repeating decimals
• Dense but not complete on the number line
• Form a field in abstract algebra