In mathematics rational means "ratio like." So a rational number is one that can be written as the ratio of two integers. For example 3=3/1, −17, and 2/3 are rational numbers.
Most real numbers (points on the number-line) are irrational (not rational). The rational numbers are those which have repeating decimal expansions (for example 1/11=0.09090909..., and 1=1.000000...=0.999999...). They are also those which have terminating continued fraction expansions. Finally, the real number x is rational if and only if there are finitely many solutions to | x − a/b | < 1/b2.