Rational numbers are numbers that can be expressed as a fraction, where both the numerator and the denominator are integers. This means that any number that can be written in the form a/b, where a and b are whole numbers and b is not zero, is considered a rational number. Examples include 1/2, 3, and -4/5. Rational numbers can be positive, negative, or zero. They can also be represented as terminating or repeating decimals. For instance, 0.75 is a terminating decimal, while 0.333... (which represents 1/3) is a repeating decimal. Understanding rational numbers is essential for various mathematical concepts and real-life applications.