Rational Numbers: Rational numbers are numbers that can be expressed as a ratio of two integers, such as fractions, whole numbers, and terminating or repeating decimals.
Irrational Numbers: Irrational numbers are numbers that cannot be expressed as a ratio of two integers, such as $\pi$, $\sqrt{2}$, and non-repeating, non-terminating decimals.
Number Line: The number line is a visual representation of the set of real numbers, where each point on the line corresponds to a unique real number.