Rational are numbers that can be represent by ratio between two integer numbers. Irrational are numbers that cannot be represent by ratio between two integer numbers. They have infinite digits after the dot. Each number having finite digits can be represent by a ratio. For instance
0.72849091471849903 = 72849091471849903/100000000000000000
also it cannot be periodic. A periodic number can be represented by a ratio. For instance
7.679499499.......499 = 767182/99900
Irrational number are, for example, Pi, e, sqrt(2)