A rational number is any number that can be expressed as a fraction, where both the numerator and the denominator are integers. The denominator cannot be zero. For example, the number 3/4 is a rational number because it can be written as a fraction of two integers: 3 and 4. Rational numbers include whole numbers, negative numbers, and fractions. Examples include 1, -2, and 5/8. Even repeating or terminating decimals, like 0.75 or 0.333..., are considered rational numbers because they can also be expressed as fractions.